Re: Do I have to use threads?

[Gary Herron]

aditya shukla wrote:

Hello people,

I have 5 directories corresponding 5  different urls .I want to 
download images from those urls and place them in the respective 
directories.I have to extract the contents and download them 
simultaneously.I can extract the contents and do then one by one. My 
questions is for doing it simultaneously do I have to use threads?


Please point me in the right direction.


Thanks

Aditya


You've been given some bad advice here.

First -- threads are lighter-weight than processes, so threads are 
probably *more* efficient.  However, with only five thread/processes, 
the difference is probably not noticeable.(If the prejudice against 
threads comes from concerns over the GIL -- that also is a misplaced 
concern in this instance.  Since you only have network connection, you 
will receive only one packet at a time, so only one thread will be 
active at a time.   If the extraction process uses a significant enough 
amount of CPU time so that the extractions are all running at the same 
time *AND* if you are running on a machine with separate CPU/cores *AND* 
you would like the extractions to be running truly in parallel on those 
separate cores,  *THEN*, and only then, will processes be more efficient 
than threads.)


Second, running 5 wgets is equivalent to 5 processes not 5 threads.

And third -- you don't have to use either threads *or* processes.  There 
is another possibility which is much more light-weight:  asynchronous 
I/O,  available through the low level select module, or more usefully 
via the higher-level asyncore module.  (Although the learning curve 
might trip you up, and some people find the programming model for 
asyncore hard to fathom,  I find it more intuitive in this case than 
threads/processes.)


In fact, the asyncore manual page has a ~20 line class which implements 
a web page retrieval.  You could replace that example's single call to 
http_client with five calls, one for each of your ULRs.  Then when you 
enter the last line (that is the asyncore.loop() call) the five  will be 
downloading simultaneously.


See http://docs.python.org/library/asyncore.html

Gary Herron

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Re: chown'ing by script

[alex23]

Carsten Haese  wrote:
> What is the underlying problem you're trying to solve with this
> approach?

To be paid for developing a web site shopping cart without actually
having to learn Python.

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Re: chown'ing by script

[Victor Subervi]

On Wed, Jan 6, 2010 at 1:41 AM, Carsten Haese wrote:

> Victor Subervi wrote:
> > Hi;
> > I have a script that is called via the web. This script writes another
> > script that is also called by the web, which in turn needs to have
> > execution privileges. The problem is that the programmatically created
> > file is owned by apache.apache and thus doesn't have execution
> > privileges. I've tried os.chown(...) but this throws an OSError. I
> > understand that chown'ing programmatically opens a big security hole.
> > However, setting the gid to give apache execution privileges isn't any
> > better. What do you suggest?
>
> I suggest you find a way to achieve whatever it is you are trying to
> achieve without having to execute programmatically created scripts. What
> is the underlying problem you're trying to solve with this approach?
>

As I was writing to respond, I re-thought the problem out and now I don't
need any more advice...at least on this issue ;) Thanks!
beno
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TypeError

[Victor Subervi]

Hi;
I get this error:

 /var/www/html/angrynates.com/christians/cart/simplemail/mail.py
  153 
  154 '''
  155 commitSale()
  156 myMail()
  157 print '''
commitSale = 
 /var/www/html/angrynates.com/christians/cart/simplemail/mail.py in
commitSale()
   98 cursor.execute('select max(ID) from %sCustomerData;' % store)
   99 custID = cursor.fetchone()[0]
  100   customerData(store, tmpTable, custID, patientID)
  101
  102 def myMail():
global customerData = , global store = 'products',
tmpTable = 'tem12627568064', custID = 1, global patientID = 'None'
 /var/www/html/angrynates.com/christians/cart/customerData.py in
customerData(store='products', tmpTable='tem12627568064', custID=1,
patientID='None')
   39 
   40 """
   41   print """
   42   print '%s Customer Data' % (store[0].upper()
+ store[1:])
   43   cursor.execute('describe %sCustomerData' % store)
store = 'products'

ValueError: unsupported format character '(' (0x28) at index 54
  args = ("unsupported format character '(' (0x28) at index 54",)

Apparently that character is a "file separator", which I presume is an
invisible character. I tried retyping the area in question, but with no
avail (threw same error). Please advise. Complete code follows.
TIA,
beno

#!/usr/bin/python

import sys,os
sys.path.append(os.getcwd())
import MySQLdb
from login import login
import re, string

def customerData(store, tmpTable, custID, patientID):
  user, passwd, db, host = login()
  db = MySQLdb.connect(host, user, passwd, db)
  cursor = db.cursor()
  page= """#!/usr/bin/python

import sys,os
sys.path.append(os.getcwd())
import MySQLdb
from login import login
import re, string
from particulars import ourStores, ourOptions
import fpformat
from sets import Set
from processOrder import processOrder

def %sCustomerData():
  print 'Content-Type: text/html'
  print
  print '''
http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd";>
http://www.w3.org/1999/xhtml";>

.text {  font-family: Arial, Helvetica, sans-serif; font-size: 16px;
text-decoration: none; text-align: justify}







"""
  print """
  print '%s Customer Data' % (store[0].upper() +
store[1:])
  cursor.execute('describe %sCustomerData' % store)
  cols = [itm[0] for itm in cursor]
  cursor.execute('select * from %sCustomerData where ID=%s' % (store,
custID))
  ourCustomerData = cursor.fetchone()
  ourColsAndCustomerDataDict = dict(zip(cols, ourCustomerData))
  for col, data in ourColsAndCustomerDataDict.iteritems():
print '%s: %s' % (col, data)
  print "Customer Order"
  print "\n  "
  numberShippingFields, totalTotal, html = processOrder(patientID, store,
tmpTable)
  print html
  print "  "
  if store != 'prescriptions':
numberCols = 12 + numberShippingFields
  else:
numberCols = 8 + numberShippingFields
  print '  \nTOTAL\n
$%s\n  ' % (numberCols - 1,
str(fpformat.fix(round(int(totalTotal * 100))/100,2)))
  print ""
  cursor.close()
  print '''


'''

%sCustomerData()
""" % (store, store)
  os.chdir('..')
  try:
os.delete('%s/%sCustomerData.py' % (os.getcwd(), store))
  except AttributeError:
pass
  file = '%sCustomerData.py' % store
  f = open(file, 'w')
  f.write(page)
  f.close()
 # os.chown('%s/%s' % (os.getcwd(), file), 500, 500)
  os.chmod('%s/%s' % (os.getcwd(), file), 0755)


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Re: Exception as the primary error handling mechanism?

[Benjamin Kaplan]

On Tue, Jan 5, 2010 at 8:45 PM, Phlip  wrote:
>
> Here's a super easy example:
>
>  { 42: 'forty two' }.get(41, None)
>
> Because I can supply a default, I can decide what is an error and what
> is .
>
> Now the equivalent in a language that does not enjoy this false "Zen":
>
>  { 42: 'forty two' }[41]  # returns None
>  { 42: 'forty two' }.fetch(41, None)  # ibid
>  { 42: 'forty two' }.fetch(41)  # raises an exception

Here's another super easy example.

Should

{42 : 'forty two'}[41]

be treated the same as

{41: None}[41] ?

In cases where None is a valid result, you can't use it to signal failure.
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Re: please help shrink this each_with_index() implementation

[alex23]

Steven D'Aprano  wrote:
> Stick around and you might learn something,
> but if you bite every time somebody tries to teach you, you'll soon run
> out of people willing to help you.

The ongoing crowdsourced development by this group of "Victor
Subervi's" project would seem to indicate that this isn't the case. Or
that if it is, that it will be a good handful of months at the very
soonest before it becomes true.
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Re: chown'ing by script

[Carsten Haese]

Victor Subervi wrote:
> Hi;
> I have a script that is called via the web. This script writes another
> script that is also called by the web, which in turn needs to have
> execution privileges. The problem is that the programmatically created
> file is owned by apache.apache and thus doesn't have execution
> privileges. I've tried os.chown(...) but this throws an OSError. I
> understand that chown'ing programmatically opens a big security hole.
> However, setting the gid to give apache execution privileges isn't any
> better. What do you suggest?

I suggest you find a way to achieve whatever it is you are trying to
achieve without having to execute programmatically created scripts. What
is the underlying problem you're trying to solve with this approach?

-Carsten

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Re: chown'ing by script

[Cameron Simpson]

On 06Jan2010 01:21, Victor Subervi  wrote:
| I have a script that is called via the web. This script writes another
| script that is also called by the web, which in turn needs to have execution
| privileges. The problem is that the programmatically created file is owned
| by apache.apache and thus doesn't have execution privileges. I've tried
| os.chown(...) but this throws an OSError. I understand that chown'ing
| programmatically opens a big security hole. However, setting the gid to give
| apache execution privileges isn't any better. What do you suggest?

Are you sure you don't want chmod?
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- Peter Harper  
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Re: Do I have to use threads?

[aditya shukla]

Thanks.i will look into multiprocessing.


Aditya
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chown'ing by script

[Victor Subervi]

Hi;
I have a script that is called via the web. This script writes another
script that is also called by the web, which in turn needs to have execution
privileges. The problem is that the programmatically created file is owned
by apache.apache and thus doesn't have execution privileges. I've tried
os.chown(...) but this throws an OSError. I understand that chown'ing
programmatically opens a big security hole. However, setting the gid to give
apache execution privileges isn't any better. What do you suggest?
TIA,
beno

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Re: [Python] Re: Printing plain text with exact positioning on Windows

[Chris Gonnerman]

KvS wrote:
Sorry, one more. I completely forgot it's not exactly plain text, but 
occasionally also a limited number of non-ASCII characters (accents in 
names etc.). Would this be possible through your method?

If Windows can print it, then MSWinPrint.py should be able to also.

But I haven't tested that extensively.  YMMV.


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Re: Minor bug in multiprocessing?

[Frank Millman]

"Aahz"  wrote:
> Frank Millman  wrote:
>>
>>Is this worth reporting, if it has not been reported already?
>
> Defiitely report it.

Thanks, Aahz.

I took the lack of responses to indicate that there was no reason *not* to 
report it, so I reported it on 24th December (issue 7571), and it was fixed 
on the same day (r77038).

Frank



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Re: Do I have to use threads?

[Brian J Mingus]

On Tue, Jan 5, 2010 at 9:36 PM, Philip Semanchuk wrote:

>
> On Jan 5, 2010, at 11:26 PM, aditya shukla wrote:
>
>  Hello people,
>>
>> I have 5 directories corresponding 5  different urls .I want to download
>> images from those urls and place them in the respective directories.I have
>> to extract the contents and download them simultaneously.I can extract the
>> contents and do then one by one. My questions is for doing it
>> simultaneously
>> do I have to use threads?
>>
>
> No. You could spawn 5 copies of wget (or curl or a Python program that
> you've written). Whether or not that will perform better or be easier to
> code, debug and maintain depends on the other aspects of your program(s).
>
> bye
> Philip


Obviously, spawning 5 copies of wget is equivalent to starting 5 threads.
The answer is 'yes'.
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Re: Do I have to use threads?

[Rodrick Brown]

On Tue, Jan 5, 2010 at 11:26 PM, aditya shukla
wrote:

> Hello people,
>
> I have 5 directories corresponding 5  different urls .I want to download
> images from those urls and place them in the respective directories.I have
> to extract the contents and download them simultaneously.I can extract the
> contents and do then one by one. My questions is for doing it simultaneously
> do I have to use threads?
>
> Please point me in the right direction.
>
> Threads in python are very easy to work with but not very efficient and for
most cases slower than running multiple processes. Look at
using multiple processes instead of going with threads performance will be
much better.


> Thanks
>
> Aditya
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
>


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Re: Exception as the primary error handling mechanism?

[Steven D'Aprano]

On Tue, 05 Jan 2010 17:45:58 -0800, Phlip wrote:

> On Jan 5, 5:01 pm, Chris Rebert  wrote:
> 
>> > Why can't int('nonnumeric') return None?
>>
>> Errors should never pass silently.
> 
> You are saying I, as the programmer, cannot decide what is an error and
> what is a pass-thru. The decision is made for me.

Every function decides for you what is an error and what isn't. 

>>> max()
Traceback (most recent call last):
  File "", line 1, in 
TypeError: max expected 1 arguments, got 0


But I wanted it to return (sys.maxint - 7). How DARE the creator of the 
language decide that it should be an error instead of returning the 
arbitrary result I choose!

Not.



> (Yes yes I can write int_or_None(), etc...)

That's right. As a programmer, your job is to program. If a language 
doesn't provide a function you want, write your own using the primitives 
available to you.



> Here's a super easy example:
> 
>   { 42: 'forty two' }.get(41, None)
> 
> Because I can supply a default, I can decide what is an error and what
> is .


You can ALWAYS decide what is an error.


d = {42: 'forty two'}
try:
d[41]
except KeyError:
print "All is good, no problems, dict does not contain 41"
except:
print "WARNING WARNING WARNING!!!"
print "FATAL ERROR: dict contains 41!!!"
sys.exit()


You do so by programming. As a programmer, that's your job.


> Now the equivalent in a language that does not enjoy this false "Zen":
> 
>   { 42: 'forty two' }[41]  # returns None

Suppose you have a dict d supplied from somewhere else. You don't know 
what's in it. You do this:

d[41]

and you get a result None. Does this mean that the dict looks like this?

d = {}

or like this?

d = {41: None}




> { 42: 'forty two' }.fetch(41, None)  # ibid 

In Python, "fetch" is spelled "get".

> { 42: 'forty two' }.fetch(41)  # raises an exception

In Python, that would be spelled {42: 'forty two'}[41]


> The quicky validation is available if I _request_ it.

When you write d[41] you are requesting it. If you don't want it, use get 
instead.



>> Quibbling over a mere one more line of code (or writing one short
>> function) seems a bit petty.
> 
> Because that "Zen of Python" is an empty sophistry that forces me to add
> a "mere one more line of code" over and over again...

If you're writing that one line of code over and over again, that's a 
good sign that you're doing it wrong and should rethink your strategy.




>> > (A related question - why can't I just go 'if record = method():  use
>> > (record)'. Why extra lines just to trap and assign the variable
>> > before using it?)
>>
>> I believe that's disallowed so as to prevent the subtle bugs seen in C
>> code which result from when someone makes a typo and omits the second
>> "=" in their `if foo == bar():` test.
> 
> Don't prevent me from using a technique just because others had trouble
> with it.


Any language allows and prevents certain techniques, simply by the very 
nature of the language. Every language has it's own syntax: you can't 
write weakly-typed stack-based concatenative code (like Forth) in Java, 
or strongly-typed dynamic object-oriented Python code in Pascal. Every 
language forces the programmer to use some features and avoid others.


> And if bar() == foo is the superior technique anyway, because the ==
> happens in chronological and lexical order after the bar() call.

That makes no sense.



-- 
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Re: please help shrink this each_with_index() implementation

[Steven D'Aprano]

On Tue, 05 Jan 2010 15:30:09 -0800, Phlip wrote:

>> > Does it say how to convert a string containing either an integer
>> > representation, or something alphabetic, into an integer, or a zero,
>> > in like 1 method call? (No except: ?)
>>
>> If you mean something like this:
>>
>> >>> int('153')
>>
>> 153
> 
> The point: int('') or int('something') both throw an error.

Well, that's a bug. Obviously they should return 42.

Or is that 23? I forget.

But seriously... of course they do. What did you expect them to do?

Any Python function will raise an exception if you pass invalid data to 
it. So the solutions are, don't pass invalid data, or wrap the function 
in a try block. If you don't want to use try, then make sure that your 
data is good.



> In general,
> this is hand-holding, but in specific I don't think the "rich and
> structured" documentation will cover how to beat a 0 out of it in less
> than 3 lines. So I will persist in my idiotic questions here!
> 
>> Then perhaps you should work through the tutorial to learn the basics.
> 
> They will tell me how to use except: (which is a good example why a
> program should not use exceptions for its normal control flow if at all
> possible).

Huh? So because YOU don't know how to use except, programs shouldn't use 
exceptions for flow control? I reject that, and I will continue using 
exceptions for flow control when I think it is appropriate.


> Please, please, please save your newbie admonitions for those who
> qualify!

Oh please, get off your high horse. You're asking newbie questions, no 
matter how many years of using Python you may or may not have, your 
experience is obviously low. Stick around and you might learn something, 
but if you bite every time somebody tries to teach you, you'll soon run 
out of people willing to help you.



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Re: Exception as the primary error handling mechanism?

[Steven D'Aprano]

On Tue, 05 Jan 2010 15:51:29 -0800, Phlip wrote:

> Why can't int('nonnumeric') return None?

It could do that, but it shouldn't, because returning magic values 
instead of raising exceptions is usually a bad, bad idea.

> (A related question - why can't I just go 'if record = method():  use
> (record)'. Why extra lines just to trap and assign the variable before
> using it?)

Because that idiom is responsible for probably the most common error in C 
of all, at least one of the most common errors. Thank goodness Python 
forbids such a dangerous construct.




-- 
Steven
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Re: Exception as the primary error handling mechanism?

[Steven D'Aprano]

On Wed, 06 Jan 2010 00:58:58 +, r0g wrote:

> Steven D'Aprano wrote:
>> On Wed, 06 Jan 2010 09:39:08 +1100, Ben Finney wrote:
>> 
>>> r0g  writes:
>>>
 Of course I'm now guilty of pedantry too :/ I might have let it slip
 had you not started your reply with the word "No", that just p*
 me off.
>>> Well, if being told “no” is going to piss you off, I think you're in
>>> for a rough time.
>> 
>> Oh, you're in trouble now! If you think he gets upset at being told no,
>> you should see how upset he gets at being told he's in for a rough
>> time!!!
>> 
>> *wink*
>> 
>> 
>> 
>> 
> 
> NO! It's a rude way to start a sentence don't you think? 

No.

I'm not Japanese, I don't feel any social prohibition at saying No in 
this context. I'm also happy to start a sentence with "You're wrong", and 
occasionally I give in to temptation to start it with "Are you on crack?".




> Just because
> you're correcting someone doesn't mean you have to be combative and try
> and make them feel small. Unless they've adopted a hostile or wilfully
> ignorant tone there's no reason to be so brusqe with people. You can be
> both nice AND terse you  know.

Now I feel hurt that you're publicly rebuking me and making me feel as if 
I've done something wrong by trying to lighten the mood with a small 
joke... 

Nah, just kidding.




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Re: Do I have to use threads?

[Philip Semanchuk]

On Jan 5, 2010, at 11:26 PM, aditya shukla wrote:


Hello people,

I have 5 directories corresponding 5  different urls .I want to  
download
images from those urls and place them in the respective  
directories.I have
to extract the contents and download them simultaneously.I can  
extract the
contents and do then one by one. My questions is for doing it  
simultaneously

do I have to use threads?


No. You could spawn 5 copies of wget (or curl or a Python program that  
you've written). Whether or not that will perform better or be easier  
to code, debug and maintain depends on the other aspects of your  
program(s).


bye
Philip

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Do I have to use threads?

[aditya shukla]

Hello people,

I have 5 directories corresponding 5  different urls .I want to download
images from those urls and place them in the respective directories.I have
to extract the contents and download them simultaneously.I can extract the
contents and do then one by one. My questions is for doing it simultaneously
do I have to use threads?

Please point me in the right direction.


Thanks

Aditya
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Re: please help shrink this each_with_index() implementation

[alex23]

Phlip  wrote:
> They will tell me how to use except: (which is a good example why a
> program should not use exceptions for its normal control flow if at
> all possible).

Really? Magic functions that coerce and eat errors are a better coding
technique than exceptions and explicit handling?

What kool-aid have you been drinking?
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Re: please help shrink this each_with_index() implementation

[MRAB]

Antoine Pitrou wrote:

The point: int('') or int('something') both throw an error. In general,
this is hand-holding, but in specific I don't think the "rich and
structured" documentation will cover how to beat a 0 out of it in less
than 3 lines.


Because it's a bad idea to do so and Python doesn't encourage such sloppy 
behaviour. If you like it, though, you might prefer PHP.


By the way: error reporting is definitely *not* hand-holding. It is 
simply not good to let errors pass silently by default. Again, if you 
think the contrary, PHP is your friend ;-)



Someone wrote about a port of a Perl script to Python. The script would
parse the output from a program it would call, but the Python script
sometimes raised a ValueError when it tried to convert a certain field
to a number. It turned out that sometimes the field would contain
"ERROR" instead of a number. The Perl script had been silently
'converting' any such "ERROR" to 0!
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Re: it gets worse (was: How do you configure IDLE on a Mac...)

[Mensanator]

On Jan 5, 4:03 pm, Ned Deily  wrote:
> In article
> <6672dad2-26ba-458b-8075-21bac6506...@e37g2000yqn.googlegroups.com>, Mensanator
>   wrote:
>
> [...]
>
>
>
>
>
> > So, for all practical purposes, the macports install is broken also.
>
> > IDLE simply does not work in an X11 window (you think someone would
> > have noticed that). The missing preferences is just the beginning.
> > Apparently NONE of the menu item shortcuts work.
>
> > For example, the Cut, Copy, Paste shortcuts are given as Command-X,
> > Command-C and Command-V. But that doesn't work in an X11 window,
> > apperently only in an Aqua Tk (parent application appears as IDLE).
>
> > Of course, I can do Control-X, Control-C and Control-V to do Cut,
> > Copy and Paste. Don't know if this works for all shortcuts, but
> > I suppose I could just pick them from the menu (and I can bang
> > my head against the wall while I'm at it).
>
> > What do you think, suppose I copy the gmpy built with the macports
> > install over to the directory where the python.org version is? Would
> > it
> > import? If that'll work, I can switch back to using the python.org
> > install and use it's version of IDLE. I certainly won't be needing
> > distutils once I have a working version of gmpy.
>
> Let's go back to your original problem, which, if I understand
> correctly, was trying to get going with Python 3 and gmpy on OS X 10.6.  

Right.

> (Sorry I was away over the holidays and didn't get a chance to respond
> to your original postings at the time.)  

Hey, no problem. I bought this dingus with the idea I would
spend my the holiday time to get it to work. Boy, was I right.

> I believe the problems you
> originally encountered with installing gmpy were all due to a couple of
> problems with building C extension modules on 10.6 when using the
> current 3.1.1 OS X python.org.  

Yeah, I used the Mac disk image for Python 3.1.

> Unfortunately, 3.1.1 was released before
> 10.6 was so there are a couple of important fixes that haven't yet been
> released for 3.1 (but are in the 2.6.4 installer which was released
> after 10.6 came out).  Fortunately, though, there are simple workarounds
> for the problems.  Keep in mind, though, that, at the moment, the
> python.org installers for OS X are 32-bit only;

I just checked, I was told to check sys.maxint but that doesn't exist,
I assume it's now sys.maxsize. On the python.org disk image, that
returns

>>> hex(sys.maxsize)
'0x7fff'

looks like 32 bits.

> that will change in the
> future but if you do need a 64-bit Python 3 you'll need to stick to
> other solutions like MacPorts for the time being.

The macports install of 3.1 gives:

>>> hex(sys.maxsize)
'07x7fff'

so the macports must be 64 bits.

>
> First, make sure the gmp library you've installed has 32-bit support.  

Uh, why would I want that? If it comes down to a choice between
IDLE and 64 bits, I'll live without IDLE.

> If you installed it using MacPorts, check with the file command:
>
> $ file /opt/local/lib/libgmp.dylib
> /opt/local/lib/libgmp.dylib: Mach-O universal binary with 2 architectures
> /opt/local/lib/libgmp.dylib (for architecture i386):  Mach-O dynamically
> linked shared library i386
> /opt/local/lib/libgmp.dylib (for architecture x86_64):   Mach-O 64-bit
> dynamically linked shared library x86_64

I get

/opt/local/lib/libgmpdylib: Mach-0 64-bit dynamically linked shared
library x86_64

>
> If it doesn't have an i386 variant, reinstall the gmp library from
> MacPorts:

But I only need that if I want to run the 32 bit version of Python
from python.org. If I'm willing to use the 64 bit version from
macports, I don't care, right?

>
> $ sudo port selfupdate    # make sure MacPorts is up-to-date
> $ sudo port clean gmp
> $ sudo port install gmp +universal     # install 32-/64-bit variants
>
> Second, you need to install the MacOSX10.4u SDK because the current
> python.org pythons are built with it.

Then I'll just not use the download from python.org. Is there a way
to uninstall that disk image?

> That SDK is included in the Snow
> Leopard Xcode installer package but it is not installed by default.  
> There should be an Xcode.mpkg somewhere, perhaps on your hard disk if
> your system came with Snow Leopard factory-installed or perhaps on a
> restore DVD.  If not, it's on the retail Snow Leopard DVD and can be
> downloaded from the Apple Developer site.  After launching the Xcode
> installer, just select and install the "Mac OS 10.4 Support" package
> from the Custom Install menu.
>
> Third, you need to tell Distutils to use the older gcc-4.0 instead of
> the gcc-4.2 which is now the default on 10.6.
>
> $ cd /path/to/gmpy-1.11rc1
> $ export CC=/usr/bin/gcc-4.0
> $ /usr/local/bin/python3.1 setup.py install
> ...
> $ /usr/local/bin/python3.1 test3/gmpy_test.py
> Unit tests for gmpy 1.11
>     on Python 3.1.1 (r311:74543, Aug 24 2009, 18:44:04)
> [GCC 4.0.1 (Apple Inc. build 5493)]
> Testing gmpy 1.11 (GMP 4.3.1), default caching (100,

Re: Exception as the primary error handling mechanism?

[Chris Rebert]

On Tue, Jan 5, 2010 at 5:45 PM, Phlip  wrote:
> On Jan 5, 5:01 pm, Chris Rebert  wrote:
>> > Why can't int('nonnumeric') return None?
>>
>> Errors should never pass silently.
>
> You are saying I, as the programmer, cannot decide what is an error
> and what is a pass-thru. The decision is made for me. (Yes yes I can
> write int_or_None(), etc...)

No, you can certainly decide yourself. You merely need be explicit
about it; you're leaving out the other tandem half of the couplet:
"*Unless* explicitly silenced." Throwing exceptions is only the
default because it tends to lead to more reliable code in that you're
forced to deal with the error condition by either catching an
exception or preventing one from being thrown (by, say, using a
different method in the API that just returns a default value
instead).

As an aside, I would guess the built-in types don't have default value
parameters for conversions partly because it'd be a bit less elegant
to implement; since None is a commonly used default value, they'd have
to use a different sentinel as said parameter's default value to
indicate that the caller wanted an exception raised, and having a
hierarchy of nil values in the core language detracts from the
language's elegance.

At any rate, if you like dict.get(), I don't see why, say,
my_int('nonnumeric', None) should be such a problem.

> Here's a super easy example:
>
>  { 42: 'forty two' }.get(41, None)
>
> Because I can supply a default, I can decide what is an error and what
> is .

Exactly, that's explicitly silencing the error; no one ever said an
`except` clause was the only silencing mechanism. You're making your
intention clear by using .get() and passing in a desired default. I
agree this is a fine thing.

> Now the equivalent in a language that does not enjoy this false "Zen":
>
>  { 42: 'forty two' }[41]  # returns None
>  { 42: 'forty two' }.fetch(41, None)  # ibid
>  { 42: 'forty two' }.fetch(41)  # raises an exception
>
> The quicky validation is available if I _request_ it.

Seems like rather "fast-and-loose" programming if you don't care about
validation enough of the time to merit it being default. If your
programming is indeed so fast-and-loose, I refer you to the recent
comment about PHP (and other less "exception-happy" languages).

Anyway, I do totally agree that you should, if feasible, be provided
an easy way to designate a common error-handling strategy (for
example, in this case, by using a default value via .fetch()).

However, go too loose on error handling and exceptions and one ends up
with something like JavaScript with its infamous `undefined` value
which can make debugging a nightmare (whoever came up with the idea of
JS's `undefined` should be slapped upside the head).

Cheers,
Chris
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Re: Minor bug in multiprocessing?

[Aahz]

[p&e]

In article ,
Frank Millman  wrote:
>
>Is this worth reporting, if it has not been reported already?

Defiitely report it.
-- 
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Weinberg's Second Law: If builders built buildings the way programmers wrote 
programs, then the first woodpecker that came along would destroy civilization.
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Re: please help shrink this each_with_index() implementation

[Antoine Pitrou]

> The point: int('') or int('something') both throw an error. In general,
> this is hand-holding, but in specific I don't think the "rich and
> structured" documentation will cover how to beat a 0 out of it in less
> than 3 lines.

Because it's a bad idea to do so and Python doesn't encourage such sloppy 
behaviour. If you like it, though, you might prefer PHP.

By the way: error reporting is definitely *not* hand-holding. It is 
simply not good to let errors pass silently by default. Again, if you 
think the contrary, PHP is your friend ;-)

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Re: Fwd: I would like to install Python on my 64 bit Win 7

[Sridhar Ratnakumar]

On 1/5/2010 11:31 AM, aung paing Soe wrote:


Hello ,
   I would like to study about Python Programming . So I want to
install Python .
But my laptop is Window 7 64-bit home basic  .
So please give me a advice how to install Python in my 64 bit computer.
I really want to study python programming .
I am looking forward your reply.
Thank you very much


Even though your laptop runs a 64-bit operating system, you do not have 
to install 64-bit Python build. You may also install a 32-bit build. 
(Some Python packages may not even build on 64-bit Python)


You can install Python from one of the two places:

1. http://python.org/download/releases/2.6.4/ (AMD64 == 64-bit)

2. http://www.activestate.com/activepython/ (Includes PyWin32, a package 
manager and extra documentation and tutorials).


-srid
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Re: parsing an Excel formula with the re module

[Steve Holden]

Tim Chase wrote:
> vsoler wrote:
>> Hence, I need to parse Excel formulas. Can I do it by means only of re
>> (regular expressions)?
>>
>> I know that for simple formulas such as "=3*A7+5" it is indeed
>> possible. What about complex for formulas that include functions,
>> sheet names and possibly other *.xls files?
> 
> Where things start getting ugly is when you have nested function calls,
> such as
> 
>   =if(Sum(A1:A25)>42,Min(B1:B25), if(Sum(C1:C25)>3.14,
> (Min(C1:C25)+3)*18,Max(B1:B25)))
> 
> Regular expressions don't do well with nested parens (especially
> arbitrarily-nesting-depth such as are possible), so I'd suggest going
> for a full-blown parsing solution like pyparsing.
> 
> If you have fair control over what can be contained in the formulas and
> you know they won't contain nested parens/functions, you might be able
> to formulate some sort of "kinda, sorta, maybe parses some forms of
> formulas" regexp.
> 
And don't forget about named ranges, which can reference cells without
using anything but a plain identifier ...

regards
 Steve
-- 
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Holden Web LLC http://www.holdenweb.com/
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Re: unittest inconsistent

[André]

On Jan 5, 8:14 pm, Matt Haggard  wrote:
> Can anyone tell me why this test fails?
>
> http://pastebin.com/f20039b17
>
> This is a minimal example of a much more complex thing I'm trying to
> do.  I'm trying to hijack a function and inspect the args passed to it
> by another function.
>
> The reason the 'Tester' object has no attribute 'arg1' is because
> "self" still refers to the object made for testA.

Quick answer: change faketest.py as follows:

#--
# faketest.py
#--

#from importme import render
import importme

def run(somearg):
return importme.render(somearg)

=
A long answer, with explanation, will cost you twice as much ;-)
(but will have to wait)

André
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Re: Exception as the primary error handling mechanism?

[Phlip]

> Errors should never pass silently.
> Unless explicitly silenced.
> -- The Zen of Python (http://www.python.org/dev/peps/pep-0020/)

"The person who says it cannot be done should never interrupt the
person doing it"
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Re: twenty years ago Guido created Python

[Daniel Fetchinson]

>>> Python is a truly awesome programming language.  Not only is Guido a
>>> genius language designer, but he is also a great project leader.  What
>>> an accomplishment.  Congratulations to everybody who has contributed
>>> to Python in the last two decades!
>>
>> The more languages you learn before getting to Smalltalk, the more
>> awesome Smalltalk will be for you.
>>
> After implementing SmallTalk I more or less gave up OO programming for
> ten years,

But why? What was so frightening about the OO model of SmallTalk?

Cheers,
Daniel

> resuming it only after I met Python. SmallTalk didn't seem
> that awesome to me.
>
> Though for its time it was an incredible system, its insistence on a
> SmallTalk-only VM environment seemed a little solipsistic.


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Re: unittest inconsistent

[Phlip]

On Jan 5, 4:14 pm, Matt Haggard  wrote:
> Can anyone tell me why this test fails?
>
> http://pastebin.com/f20039b17
>
> This is a minimal example of a much more complex thing I'm trying to
> do.  I'm trying to hijack a function and inspect the args passed to it
> by another function.
>
> The reason the 'Tester' object has no attribute 'arg1' is because
> "self" still refers to the object made for testA.

I hope someone else can spot the low-level reason...

...but why aren't you using http://pypi.python.org/pypi/mock/ ? Look
up its patch_object facility...
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Re: Exception as the primary error handling mechanism?

[Phlip]

On Jan 5, 5:01 pm, Chris Rebert  wrote:

> > Why can't int('nonnumeric') return None?
>
> Errors should never pass silently.

You are saying I, as the programmer, cannot decide what is an error
and what is a pass-thru. The decision is made for me. (Yes yes I can
write int_or_None(), etc...)

Here's a super easy example:

  { 42: 'forty two' }.get(41, None)

Because I can supply a default, I can decide what is an error and what
is .

Now the equivalent in a language that does not enjoy this false "Zen":

  { 42: 'forty two' }[41]  # returns None
  { 42: 'forty two' }.fetch(41, None)  # ibid
  { 42: 'forty two' }.fetch(41)  # raises an exception

The quicky validation is available if I _request_ it.

> Quibbling over a mere one more line of code (or writing one short
> function) seems a bit petty.

Because that "Zen of Python" is an empty sophistry that forces me to
add a "mere one more line of code" over and over again...

> > (A related question - why can't I just go 'if record = method():  use
> > (record)'. Why extra lines just to trap and assign the variable before
> > using it?)
>
> I believe that's disallowed so as to prevent the subtle bugs seen in C
> code which result from when someone makes a typo and omits the second
> "=" in their `if foo == bar():` test.

Don't prevent me from using a technique just because others had
trouble with it.

And if bar() == foo is the superior technique anyway, because the ==
happens in chronological and lexical order after the bar() call.
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Re: Exception as the primary error handling mechanism?

[r0g]

Lie Ryan wrote:
> On 1/6/2010 1:48 AM, r0g wrote:
>> Steven D'Aprano wrote:
>>> On Tue, 05 Jan 2010 13:06:20 +, r0g wrote:
 If
 that's the case how can you expect it to validate anything at all in
 production?
>>>
>>> The asserts still operate so long as you don't use the -O switch.
>>>

> checking, since the function relies on the caller obeying the
> contract[2] and never calling it with an invalid input.
> 
> DbC uses assertions[1] spuriously, unlike the traditional approach which
> is much more conservative when using assertions.
> 
> [1] or explicit language support which is just syntax sugar for assertions
> [2] of course, on a debug release, the contract validation code will
> still be enforced to catch logic/consistency bugs that causes the violation


Thanks for the responses Steven/Dave/Lie, that's some really insightful
stuff :)

Roger.
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Re: Exception as the primary error handling mechanism?

[Chris Rebert]

On Tue, Jan 5, 2010 at 3:51 PM, Phlip  wrote:
> Peng Yu wrote:
>> Otherwise, could some python expert explain to me why exception is
>> widely used for error handling in python? Is it because the efficiency
>> is not the primary goal of python?
>
> It's not about efficiency, it's about making assumptions for the
> programmer about what kind of rigor they need.
>
> Why can't int('nonnumeric') return None?

Errors should never pass silently.
Unless explicitly silenced.
-- The Zen of Python (http://www.python.org/dev/peps/pep-0020/)

Better to throw an exception and ensure the case is specifically dealt
with one way or another than to silently return an error flag result
which may only delay the error until later in the program, making it
harder to debug. Is it that much of a burden to write and use the
small function that does what you want?

def int_or_None(string):
try:
return int(string)
except ValueError:
return None

Heck, you can even write it inline and dispense with the function if you want:

try: foo = int(bar)
except ValueError: foo = None

Quibbling over a mere one more line of code (or writing one short
function) seems a bit petty.

> (A related question - why can't I just go 'if record = method():  use
> (record)'. Why extra lines just to trap and assign the variable before
> using it?)

I believe that's disallowed so as to prevent the subtle bugs seen in C
code which result from when someone makes a typo and omits the second
"=" in their `if foo == bar():` test.

Cheers,
Chris
--
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Re: Exception as the primary error handling mechanism?

[r0g]

Steven D'Aprano wrote:
> On Wed, 06 Jan 2010 09:39:08 +1100, Ben Finney wrote:
> 
>> r0g  writes:
>>
>>> Of course I'm now guilty of pedantry too :/ I might have let it slip
>>> had you not started your reply with the word "No", that just p* me
>>> off.
>> Well, if being told “no” is going to piss you off, I think you're in for
>> a rough time.
> 
> Oh, you're in trouble now! If you think he gets upset at being told no, 
> you should see how upset he gets at being told he's in for a rough time!!!
> 
> *wink*
> 
> 
> 


NO! It's a rude way to start a sentence don't you think? Just because
you're correcting someone doesn't mean you have to be combative and try
and make them feel small. Unless they've adopted a hostile or wilfully
ignorant tone there's no reason to be so brusqe with people. You can be
both nice AND terse you  know.

I can't imagine why I expect good manners on usenet though, AFAICT it's
never been like that (well not since I got on it anyway).

Roger.


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Re: please help shrink this each_with_index() implementation

[Mackrackit]

On Jan 5, 2010, at 4:30 PM, Phlip  wrote:





The point: int('') or int('something') both throw an error. In
general, this is hand-holding, but in specific I don't think the "rich
and structured" documentation will cover how to beat a 0 out of it in
less than 3 lines. So I will persist in my idiotic questions here!



What does an extra two or three lines of code matter?

Dave-- 
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Re: subprocess.Popen does not close pipe in an error case

[Steven K. Wong]

BTW, I'm using Python 2.6.2 on Linux.
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Re: Exception as the primary error handling mechanism?

[Phlip]

Peng Yu wrote:

> Otherwise, could some python expert explain to me why exception is
> widely used for error handling in python? Is it because the efficiency
> is not the primary goal of python?

It's not about efficiency, it's about making assumptions for the
programmer about what kind of rigor they need.

Why can't int('nonnumeric') return None?

Why can't a Django Record.objects.get(pk=-1) return a None? That's
what it's for.

(A related question - why can't I just go 'if record = method():  use
(record)'. Why extra lines just to trap and assign the variable before
using it?)

There are workarounds that sometimes benefit the code. In the case of
collections, like recordsets, you might be better off using for ... all
():

Then your controlled block efficiently does not happen if it saw no
records. "Efficiently" in terms of programmer complexity - the number
and meaning of lines that a programmer must comprehend.

And why can't Record.objects.get(pk='nonnumeric') return None?
Because, of course, deep inside it calls int(). I can't simplify the
calling code, and rely on garbage-in-None-out, because Python decided
which simplifications I should avoid with self-righteous indignation.

The Samurai Principle (return victorious, or not at all) is very
useful, sometimes. But other times it just prematurely depletes your
supply of Samurai...

--
  Phlip
  http://zeekland.zeroplayer.com/
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subprocess.Popen does not close pipe in an error case

[Steven K. Wong]

Below, I have a Python script that launches 2 child programs, prog1
and prog2, with prog1's stdout connected to prog2's stdin via a pipe.
(It's like executing "prog1 | prog2" in the shell.)

If both child programs exit with 0, then the script runs to
completion. But if prog2 exits with non-0, prog1 does not exit and the
script hangs (i.e. prog1.poll() always returns None) -- unless I
uncomment the 2 lines marked by XXX to close prog1.stdout.

I was expecting that I don't have to explicitly close prog1.stdout,
whether prog2 succeeds or fails. Is the current behavior a bug in the
subprocess module or is it expected? Or am I doing something wrong?

Thanks.

import subprocess
import time

# prog1: a program that writes lots of data to the pipe
cmd = ['zcat', '--force', 'a_large_file']
prog1 = subprocess.Popen(cmd, bufsize=-1, stdout=subprocess.PIPE)

# prog2: a program that fails without reading much data from the pipe
cmd = ['python', '-c', 'import time; time.sleep(10); asdf']
prog2 = subprocess.Popen(cmd, bufsize=-1, stdin=prog1.stdout,
stdout=open('popen.out', 'w'))
print 'waiting for a while'

retCodeProg2 = prog2.wait()
print 'prog2 returns', retCodeProg2
# XXX
# if retCodeProg2 != 0:
# prog1.stdout.close()
while prog1.poll() is None:
print 'sleep a bit'
time.sleep(1)
retCodeProg1 = prog1.poll()
print 'prog1 returns', retCodeProg1
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Re: please help shrink this each_with_index() implementation

[Phlip]

> > Does it say how to convert a string containing either an integer
> > representation, or something alphabetic, into an integer, or a zero, in
> > like 1 method call? (No except: ?)
>
> If you mean something like this:
>
> >>> int('153')
>
> 153

The point: int('') or int('something') both throw an error. In
general, this is hand-holding, but in specific I don't think the "rich
and structured" documentation will cover how to beat a 0 out of it in
less than 3 lines. So I will persist in my idiotic questions here!

> Then perhaps you should work through the tutorial to learn the basics.

They will tell me how to use except: (which is a good example why a
program should not use exceptions for its normal control flow if at
all possible).

Please, please, please save your newbie admonitions for those who
qualify!
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Re: please help shrink this each_with_index() implementation

[Steven D'Aprano]

On Tue, 05 Jan 2010 14:40:49 -0800, Phlip wrote:

> On Jan 5, 1:10 pm, Antoine Pitrou  wrote:
> 
>> http://docs.python.org/library/functions.html
>>
>> Don't forget that the Python documentation is rich and structured. And
>> good luck.
> 
> Does it say how to convert a string containing either an integer
> representation, or something alphabetic, into an integer, or a zero, in
> like 1 method call? (No except: ?)

If you mean something like this:

>>> int('153')
153

then yes it does. But if you mean something like this:


>>> some_mysterious_function('one hundred and fifty-three')
153

then no, it doesn't.



> Nothing personal, but I'm finding the super-hard stuff very facile &
> tractable, and the easy stuff absurdly hard around here...


Then perhaps you should work through the tutorial to learn the basics.



-- 
Steven
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Re: Exception as the primary error handling mechanism?

[Steven D'Aprano]

On Wed, 06 Jan 2010 09:39:08 +1100, Ben Finney wrote:

> r0g  writes:
> 
>> Of course I'm now guilty of pedantry too :/ I might have let it slip
>> had you not started your reply with the word "No", that just p* me
>> off.
> 
> Well, if being told “no” is going to piss you off, I think you're in for
> a rough time.

Oh, you're in trouble now! If you think he gets upset at being told no, 
you should see how upset he gets at being told he's in for a rough time!!!

*wink*



-- 
Steven
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Re: Python multiprocessing: Permission denied

[Steven D'Aprano]

On Tue, 05 Jan 2010 13:52:18 -0800, t0ster wrote:

> It looks like the user don't have permission to access shared memory.
> When executing with root privileges it works fine.
> 
> Is there any solution to run it as normal user(not root)?

Then give the user permission to access shared memory.

Why do you expect that Python would be able to over-ride the operating 
system's security? This problem is no different from saying "It looks 
like the user doesn't have permission to access this file".


-- 
Steven
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Re: please help shrink this each_with_index() implementation

[Phlip]

On Jan 5, 1:10 pm, Antoine Pitrou  wrote:

> http://docs.python.org/library/functions.html
>
> Don't forget that the Python documentation is rich and structured.
> And good luck.

Does it say how to convert a string containing either an integer
representation, or something alphabetic, into an integer, or a zero,
in like 1 method call? (No except: ?)

Nothing personal, but I'm finding the super-hard stuff very facile &
tractable, and the easy stuff absurdly hard around here...
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Re: Exception as the primary error handling mechanism?

[Ben Finney]

r0g  writes:

> Of course I'm now guilty of pedantry too :/ I might have let it slip
> had you not started your reply with the word "No", that just p* me
> off.

Well, if being told “no” is going to piss you off, I think you're in for
a rough time.

> Having said that I find the mental image of you slamming your fist on
> the table and shouting it out loud whenever you read something you
> disagree with on usenet quite amusing!

In return, I find myself quite amused that you would get such an image.
To reduce the stress you describe above, you might want to read what is
written, rather than inventing fanciful emotion where it wasn't in the
message to begin with.

-- 
 \  “One time I went to a drive-in in a cab. The movie cost me |
  `\  ninety-five dollars.” —Steven Wright |
_o__)  |
Ben Finney
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Re: parsing an Excel formula with the re module

[MRAB]

Mensanator wrote:

On Jan 5, 12:35 pm, MRAB  wrote:

vsoler wrote:

Hello,
I am acessing an Excel file by means of Win 32 COM technology.
For a given cell, I am able to read its formula. I want to make a map
of how cells reference one another, how different sheets reference one
another, how workbooks reference one another, etc.
Hence, I need to parse Excel formulas. Can I do it by means only of re
(regular expressions)?
I know that for simple formulas such as "=3*A7+5" it is indeed
possible. What about complex for formulas that include functions,
sheet names and possibly other *.xls files?
For example"=Book1!A5+8" should be parsed into ["=","Book1", "!",
"A5","+","8"]
Can anybody help? Any suggestions?

Do you mean "how" or do you really mean "whether", ie, get a list of the
other cells that are referred to by a certain cell, for example,
"=3*A7+5" should give ["A7"] and "=Book1!A5+8" should give ["Book1!A5]


Ok, although "Book1" would be the default name of a workbook, with
default
worksheets labeled "Sheet1". "Sheet2", etc.

If I had a worksheet named "Sheety" that wanted to reference a cell on
"Sheetx"
OF THE SAME WORKBOOK, it would be =Sheet2!A7. If the reference was to
a completely
different workbook (say Book1 with worksheets labeled "Sheet1",
"Sheet2") then
the cell might have =[Book1]Sheet1!A7.

And don't forget the $'s! You may see =[Book1]Sheet1!$A$7.


I forgot about the dollars! In that case, the regex is:

references = re.findall(r"\b((?:\w+!)?\$?[A-Za-z]+\$?\d+)\b", formula)
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Re: it gets worse (was: How do you configure IDLE on a Mac...)

[Ned Deily]

In article 
<6672dad2-26ba-458b-8075-21bac6506...@e37g2000yqn.googlegroups.com>,
 Mensanator  wrote:
[...]
> So, for all practical purposes, the macports install is broken also.
> 
> IDLE simply does not work in an X11 window (you think someone would
> have noticed that). The missing preferences is just the beginning.
> Apparently NONE of the menu item shortcuts work.
> 
> For example, the Cut, Copy, Paste shortcuts are given as Command-X,
> Command-C and Command-V. But that doesn't work in an X11 window,
> apperently only in an Aqua Tk (parent application appears as IDLE).
> 
> Of course, I can do Control-X, Control-C and Control-V to do Cut,
> Copy and Paste. Don't know if this works for all shortcuts, but
> I suppose I could just pick them from the menu (and I can bang
> my head against the wall while I'm at it).
> 
> What do you think, suppose I copy the gmpy built with the macports
> install over to the directory where the python.org version is? Would
> it
> import? If that'll work, I can switch back to using the python.org
> install and use it's version of IDLE. I certainly won't be needing
> distutils once I have a working version of gmpy.

Let's go back to your original problem, which, if I understand 
correctly, was trying to get going with Python 3 and gmpy on OS X 10.6.   
(Sorry I was away over the holidays and didn't get a chance to respond 
to your original postings at the time.)  I believe the problems you 
originally encountered with installing gmpy were all due to a couple of 
problems with building C extension modules on 10.6 when using the 
current 3.1.1 OS X python.org.  Unfortunately, 3.1.1 was released before 
10.6 was so there are a couple of important fixes that haven't yet been 
released for 3.1 (but are in the 2.6.4 installer which was released 
after 10.6 came out).  Fortunately, though, there are simple workarounds 
for the problems.  Keep in mind, though, that, at the moment, the 
python.org installers for OS X are 32-bit only; that will change in the 
future but if you do need a 64-bit Python 3 you'll need to stick to 
other solutions like MacPorts for the time being.

First, make sure the gmp library you've installed has 32-bit support.  
If you installed it using MacPorts, check with the file command:

$ file /opt/local/lib/libgmp.dylib
/opt/local/lib/libgmp.dylib: Mach-O universal binary with 2 architectures
/opt/local/lib/libgmp.dylib (for architecture i386):  Mach-O dynamically 
linked shared library i386
/opt/local/lib/libgmp.dylib (for architecture x86_64):   Mach-O 64-bit 
dynamically linked shared library x86_64

If it doesn't have an i386 variant, reinstall the gmp library from 
MacPorts:

$ sudo port selfupdate# make sure MacPorts is up-to-date
$ sudo port clean gmp
$ sudo port install gmp +universal # install 32-/64-bit variants

Second, you need to install the MacOSX10.4u SDK because the current 
python.org pythons are built with it.  That SDK is included in the Snow 
Leopard Xcode installer package but it is not installed by default.  
There should be an Xcode.mpkg somewhere, perhaps on your hard disk if 
your system came with Snow Leopard factory-installed or perhaps on a 
restore DVD.  If not, it's on the retail Snow Leopard DVD and can be 
downloaded from the Apple Developer site.  After launching the Xcode 
installer, just select and install the "Mac OS 10.4 Support" package 
from the Custom Install menu.

Third, you need to tell Distutils to use the older gcc-4.0 instead of 
the gcc-4.2 which is now the default on 10.6.

$ cd /path/to/gmpy-1.11rc1
$ export CC=/usr/bin/gcc-4.0
$ /usr/local/bin/python3.1 setup.py install
...
$ /usr/local/bin/python3.1 test3/gmpy_test.py
Unit tests for gmpy 1.11
on Python 3.1.1 (r311:74543, Aug 24 2009, 18:44:04) 
[GCC 4.0.1 (Apple Inc. build 5493)]
Testing gmpy 1.11 (GMP 4.3.1), default caching (100, 128)
...
1500 tests in 42 items.
1500 passed and 0 failed.

-- 
 Ned Deily,
 n...@acm.org

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Python multiprocessing: Permission denied

[t0ster]

Hi guys, I'm getting an error when trying to execute python program
that uses multiprocessing package:

  File "/usr/local/lib/python2.6/multiprocessing/__init__.py", line
178, in RLock
return RLock()
  File "/usr/local/lib/python2.6/multiprocessing/synchronize.py", line
142, in __init__
SemLock.__init__(self, RECURSIVE_MUTEX, 1, 1)
  File "/usr/local/lib/python2.6/multiprocessing/synchronize.py", line
49, in __init__
sl = self._semlock = _multiprocessing.SemLock(kind, value,
maxvalue)
OSError: [Errno 13] Permission denied

It looks like the user don't have permission to access shared memory.
When executing with root privileges it works fine.

Is there any solution to run it as normal user(not root)?

Python version 2.6.2 , OS is Linux 2.6.18 (CentOS release 5.4) and
it's VPS machine.
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Re: Dynamic text color

[Dave McCormick]

John Posner wrote:
On Tue, 05 Jan 2010 15:08:04 -0500, Dave McCormick 
 wrote:


It sounds like the program is doing exactly what you TOLD it to do 
(which might not be what you WANT it to do):


 1. In an earlier pass on the text, color the string "dog" red.
 2. In a later pass, color the string "do" green.

You need to decide what you WANT to happen if one word to be colored 
is a substring of another word to be colored differently. Or maybe you 
want to outlaw such situations. After making that decision, you can 
start to think about how to write the appropriate code.


Best,
John
Darn thing doing what I told it to do...  Guess that means I did 
something right :)
But it is not what I am wanting. 
I first thought to make it look for a space but that would not work when 
a single character like "#" is to be colored if there is a "string" of 
them.  Or if all of the characters between quotes are to be colored. 


I always did like puzzles!

Dave
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Commands for a breakpoint in .pdbrc

[Pablo Torres N.]

Hi all,

I'd like to save the commands for a breakpoint in a .pdbrc, something
like:

b 81
commands 1
pp foo.attr1
pp foo.attr2
end
b 108
commands 2
pp bar.attr1
pp bar.attr2
end

This would automate setting the environment for the debugging session.
However, this does not work with 'python -m pdb script.py', because at
the line 'commands 1', the pdb prompt starts and asks me for the
commands for the first breakpoint, ignoring what I wrote in .pdbrc;
further, it raises a NameError after I type 'end' at the pdb prompt,
because of 'foo.attr1', 'foo.attr2' and even 'end'. The same happens
for the rest of the breakpoints, so I end up with them set but not
their commands.

What would be the correct way to do this? Is it even possible?


Thanks a lot,
Pablo Torres N.
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Re: A null program - what is it doing?

[Gib Bogle]

r0g wrote:

Gib Bogle wrote:

No doubt a dumb question from a noob:

The following program (a cut down version of some test code) uses no
CPU, and does not terminate:

import sys
from PyQt4.QtCore import *

if __name__=="__main__":
app = QCoreApplication(sys.argv)
sys.exit(app.exec_())

What is the program doing?  What is the correct way to terminate the
execution?

Thanks in advance for educating me.




I've never used QT but other graphical toolkits I have used all start
their own "main loop" which is a loop that cycles round receiving,
queuing and dispatching "events". You probably need to call the
QCoreApplication's quit method to break out of this e.g.

app.exit() or something similar, have a look at some complete PyQt4
examples or google for PyQt4 mainloop.


Roger.


Thanks.  I've realized that QCoreApplication (or QApplication) manages the event 
loop, and normally when it is executed you are showing a widget of some kind, 
closing which ends the application.  Alt-F4 acts like Ctrl-C to terminate from 
the keyboard.

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Re: please help shrink this each_with_index() implementation

[Antoine Pitrou]

>> Couldn't you just use the built-in enumerate() to replace the whole
>> thing?
> 
> Because that would involve, like, reading an entire Python book just to
> locate that method?

Actually, no. It just involves reading one of the most important pages in 
the documentation, the page which describes the built-in functions:

http://docs.python.org/library/functions.html

Don't forget that the Python documentation is rich and structured.
And good luck.


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Re: please help shrink this each_with_index() implementation

[Phlip]

> > My Pythonic sequencing skills are obviously feeble. Can anything think
> > of a way to write that in fewer lines?

Thanks, all!

> Couldn't you just use the built-in enumerate() to replace the whole thing?

Because that would involve, like, reading an entire Python book just
to locate that method?

GMAB I'm too busy writing high-end Django via TDD & BDD! C-:

--
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  http://zeekland.zeroplayer.com/Pigleg_Too/1
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Re: Dynamic text color

[John Posner]

On Tue, 05 Jan 2010 15:08:04 -0500, Dave McCormick   
wrote:




It's certainly a mistake to use the expression "str(rList).split()".  
Using str() to convert the list "rList" into a string creates a mess  
that includes square-bracket characters. Did this actually work for you?


It sort of worked.  With one color file it seemed fine but after I  
posted I added another color file and things fell apart.
Now with the above fixes it works with three colors from three files.   
When the list are printed to the shell the list look like this:

redList ['red', 'dog', 'apple', '#']
blueList ['blue', 'ball', 'berry']
greenList ['green', 'grass', 'do']

But another problem is noticed.  It does not matter if the list is built  
in code or from a file.
If dog is entered, "do" will be green with the "g" being red.  Back to  
the drawing board.


It sounds like the program is doing exactly what you TOLD it to do (which  
might not be what you WANT it to do):


 1. In an earlier pass on the text, color the string "dog" red.
 2. In a later pass, color the string "do" green.

You need to decide what you WANT to happen if one word to be colored is a  
substring of another word to be colored differently. Or maybe you want to  
outlaw such situations. After making that decision, you can start to think  
about how to write the appropriate code.


Best,
John
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Re: please help shrink this each_with_index() implementation

[Marco Nawijn]

On Jan 5, 8:58 pm, Phlip  wrote:
> Hypo Nt:
>
> def each_with_index(seq):
>     index = 0
>     result = []
>
>     for item in seq:
>       result.append([item, index])
>       index += 1
>
>     return result
>
> My Pythonic sequencing skills are obviously feeble. Can anything think
> of a way to write that in fewer lines?
>
> --
>   Phlip
>  http://c2.com/cgi/wiki?MoreliaViridis

You could use the build-in function enumerate inside a list
comprehension.

>>> seq = range(5)
>>> [ (i,s) for i,s in enumerate(seq) ]
[(0, 0), (1, 1), (2, 2), (3, 3), (4, 4)]

This will reduce the function to a one-liner.

Regards,

Marco
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Re: please help shrink this each_with_index() implementation

[Carsten Haese]

Phlip wrote:
> Hypo Nt:
> 
> def each_with_index(seq):
> index = 0
> result = []
> 
> for item in seq:
>   result.append([item, index])
>   index += 1
> 
> return result
> 
> My Pythonic sequencing skills are obviously feeble. Can anything think
> of a way to write that in fewer lines?

Couldn't you just use the built-in enumerate() to replace the whole thing?

--
Carsten Haese
http://informixdb.sourceforge.net

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Re: please help shrink this each_with_index() implementation

[akean]

On Jan 6, 8:58 am, Phlip  wrote:
> Hypo Nt:
>
> def each_with_index(seq):
>     index = 0
>     result = []
>
>     for item in seq:
>       result.append([item, index])
>       index += 1
>
>     return result
>
> My Pythonic sequencing skills are obviously feeble. Can anything think
> of a way to write that in fewer lines?
>
> --
>   Phlip
>  http://c2.com/cgi/wiki?MoreliaViridis

 y = [[seq[i],i] for i in range(len(seq))]  gives the same result.
The index is accessible without assigning it to another variable.
--
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Re: Fwd: I would like to install Python on my 64 bit Win 7

[Benjamin Kaplan]

On Tue, Jan 5, 2010 at 3:03 PM, Dave McCormick  wrote:
>
>
> aung paing Soe wrote:
>
> -- Forwarded message --
> From: aung paing Soe 
> Date: Tue, Jan 5, 2010 at 11:27 AM
> Subject: I would like to install Python on my 64 bit Win 7
> To: webmas...@python.org
>
>
> Hello ,
>   I would like to study about Python Programming . So I want to
> install Python .
> But my laptop is Window 7 64-bit home basic  .
> So please give me a advice how to install Python in my 64 bit computer.
> I really want to study python programming .
> I am looking forward your reply.
> Thank you very much
>
> Yours,
> Beginner
>
> I am using WIN7 64 bit also.
> Go to python.org and look for
> http://www.python.org/download/releases/2.5.4/
> python-2.5.4.amd64.msi
>
> Dave

Unless you need a package that requires Python 2.5, it's a good idea
to use Python 2.6 instead. 2.5 isn't getting any more bug fixes and
2.6 includes quite a few new features.
http://python.org/download/releases/2.6.4/
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
>
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Re: twenty years ago Guido created Python

[Mensanator]

On Jan 5, 8:22 am, n00m  wrote:
> Stick your English into your ass

Most people would say "up your ass".
And use a period at the end of the sentence.

Got any more funny insults?
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Re: Dynamic text color

[Dave McCormick]

John Posner wrote:


Dave, you're doing exactly the right thing: gradually expanding your 
program, to provide more functionality and to learn more about the 
available programming tools. It's also very good that you take care to 
close() the file after processing it. Now for the bad news ...

Seems like there is always bad news :)


1. Don't use "file" as a variable name -- it's a built-in object type. 
(Some people don't like the fact that Python allows you to redefine 
such "reserved words".)


2. It's probably not the best idea to use a single variable (you use 
"file") to do double-duty: to hold the name of a file, and to hold the 
open-file object returned by the open() function. It's perfectly 
legal, but it hides information that might be useful when you're 
debugging a program. This is better:


3. It might be better to use read() rather than readlines() to process 
the "red.txt" file. It depends on what that file is supposed to 
contain. For example, if you expect "red.txt" to contain exactly one 
line, which has one or more words, you can process the open-file 
object like this:

All noted and fixed.


It's certainly a mistake to use the expression "str(rList).split()". 
Using str() to convert the list "rList" into a string creates a mess 
that includes square-bracket characters. Did this actually work for you?
It sort of worked.  With one color file it seemed fine but after I 
posted I added another color file and things fell apart.
Now with the above fixes it works with three colors from three files.  
When the list are printed to the shell the list look like this:

redList ['red', 'dog', 'apple', '#']
blueList ['blue', 'ball', 'berry']
greenList ['green', 'grass', 'do']

But another problem is noticed.  It does not matter if the list is built 
in code or from a file.
If dog is entered, "do" will be green with the "g" being red.  
Back to the drawing board.


Here is the complete code"
##
from Tkinter import *
import re
RFfile = 'red.txt'
inpRF = open(RFfile,"r")
rList = inpRF.read()
inpRF.close()

BFfile = 'blue.txt'
inpBF = open(BFfile,"r")
bList = inpBF.read()
inpBF.close()

GFfile = 'green.txt'
inpGF = open(GFfile,"r")
gList = inpGF.read()
inpGF.close()

def get_complete_text(event):
   complete_text = Tbox.get("1.0", END)
   redList = str(rList).split()
   blueList = str(bList).split()
   greenList = str(gList).split()
   print "redList",redList
   print "blueList",blueList
   print "greenList",greenList
   Tbox.tag_remove("red", "1.0", END)
   Tbox.tag_remove("blue", "1.0", END)
   Tbox.tag_remove("green", "1.0", END)
RED
   redList_regexp = "|".join(redList)
   for matchobj in re.finditer(redList_regexp, complete_text):
   start,end = matchobj.span()
   Tbox.tag_add("red", "1.0 + %d chars" % start,"1.0 + %d chars" % end)
   Tbox.tag_config("red", foreground="red")
BLUE###
   blueList_regexp = "|".join(blueList)
   for matchobj in re.finditer(blueList_regexp, complete_text):
   start,end = matchobj.span()
   Tbox.tag_add("blue", "1.0 + %d chars" % start,"1.0 + %d chars" % 
end)

   Tbox.tag_config("blue", foreground="blue")
GREEN###
   greenList_regexp = "|".join(greenList)
   for matchobj in re.finditer(greenList_regexp, complete_text):
   start,end = matchobj.span()
   Tbox.tag_add("green", "1.0 + %d chars" % start,"1.0 + %d chars" 
% end)

   Tbox.tag_config("green", foreground="green")

root = Tk()
Tbox = Text(root, width=40, height=15, wrap=CHAR,
  font="Times 14 bold", bg="#dd")
Tbox.pack()
Tbox.bind("", get_complete_text)
Tbox.focus()
root.mainloop()

Thanks again,
Dave
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Re: Fwd: I would like to install Python on my 64 bit Win 7

[Dave McCormick]

aung paing Soe wrote:

  
  -- Forwarded message --
From: aung paing Soe 
Date: Tue, Jan 5, 2010 at 11:27 AM
Subject: I would like to install Python on my 64 bit Win 7
To: webmas...@python.org
  
  
Hello , 
  I would like to study about Python Programming . So I want to
install Python .
But my laptop is Window 7 64-bit home basic  . 
So please give me a advice how to install Python in my 64 bit computer.
I really want to study python programming .
I am looking forward your reply.
Thank you very much
  
Yours, 
Beginner 
  

I am using WIN7 64 bit also.  
Go to python.org and look for 
http://www.python.org/download/releases/2.5.4/
python-2.5.4.amd64.msi

Dave


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please help shrink this each_with_index() implementation

[Phlip]

Hypo Nt:

def each_with_index(seq):
index = 0
result = []

for item in seq:
  result.append([item, index])
  index += 1

return result

My Pythonic sequencing skills are obviously feeble. Can anything think
of a way to write that in fewer lines?

--
  Phlip
  http://c2.com/cgi/wiki?MoreliaViridis
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Re: parsing an Excel formula with the re module

[vsoler]

On 5 ene, 20:21, vsoler  wrote:
> On 5 ene, 20:05, Mensanator  wrote:
>
>
>
> > On Jan 5, 12:35 pm, MRAB  wrote:
>
> > > vsoler wrote:
> > > > Hello,
>
> > > > I am acessing an Excel file by means of Win 32 COM technology.
> > > > For a given cell, I am able to read its formula. I want to make a map
> > > > of how cells reference one another, how different sheets reference one
> > > > another, how workbooks reference one another, etc.
>
> > > > Hence, I need to parse Excel formulas. Can I do it by means only of re
> > > > (regular expressions)?
>
> > > > I know that for simple formulas such as "=3*A7+5" it is indeed
> > > > possible. What about complex for formulas that include functions,
> > > > sheet names and possibly other *.xls files?
>
> > > > For example    "=Book1!A5+8" should be parsed into ["=","Book1", "!",
> > > > "A5","+","8"]
>
> > > > Can anybody help? Any suggestions?
>
> > > Do you mean "how" or do you really mean "whether", ie, get a list of the
> > > other cells that are referred to by a certain cell, for example,
> > > "=3*A7+5" should give ["A7"] and "=Book1!A5+8" should give ["Book1!A5]
>
> > Ok, although "Book1" would be the default name of a workbook, with
> > default
> > worksheets labeled "Sheet1". "Sheet2", etc.
>
> > If I had a worksheet named "Sheety" that wanted to reference a cell on
> > "Sheetx"
> > OF THE SAME WORKBOOK, it would be =Sheet2!A7. If the reference was to
> > a completely
> > different workbook (say Book1 with worksheets labeled "Sheet1",
> > "Sheet2") then
> > the cell might have =[Book1]Sheet1!A7.
>
> > And don't forget the $'s! You may see =[Book1]Sheet1!$A$7.
>
> Yes, Mensanator, but...  what re should I use? I'm looking for the re
> statement. No doubt you can help!
>
> Thank you.


Let me give you an example:

>>> import re
>>> re.split("([^0-9])", "123+456*/")
[’123’, ’+’, ’456’, ’*’, ’’, ’/’, ’’]

I find it excellent that one single statement is able to do a lexical
analysis of an expression!

If the expression contains variables, such as A12 or B9, I can try
another re expression. Which one should I use?

And if my expression contains parenthesis?   And the sin() function?

Vicente Soler


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Re: parsing an Excel formula with the re module

[Tim Chase]

vsoler wrote:

Hence, I need to parse Excel formulas. Can I do it by means only of re
(regular expressions)?

I know that for simple formulas such as "=3*A7+5" it is indeed
possible. What about complex for formulas that include functions,
sheet names and possibly other *.xls files?


Where things start getting ugly is when you have nested function 
calls, such as


  =if(Sum(A1:A25)>42,Min(B1:B25), if(Sum(C1:C25)>3.14, 
(Min(C1:C25)+3)*18,Max(B1:B25)))


Regular expressions don't do well with nested parens (especially 
arbitrarily-nesting-depth such as are possible), so I'd suggest 
going for a full-blown parsing solution like pyparsing.


If you have fair control over what can be contained in the 
formulas and you know they won't contain nested parens/functions, 
you might be able to formulate some sort of "kinda, sorta, maybe 
parses some forms of formulas" regexp.


-tkc


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Fwd: I would like to install Python on my 64 bit Win 7

[aung paing Soe]

-- Forwarded message --
From: aung paing Soe 
Date: Tue, Jan 5, 2010 at 11:27 AM
Subject: I would like to install Python on my 64 bit Win 7
To: webmas...@python.org


Hello ,
  I would like to study about Python Programming . So I want to
install Python .
But my laptop is Window 7 64-bit home basic  .
So please give me a advice how to install Python in my 64 bit computer.
I really want to study python programming .
I am looking forward your reply.
Thank you very much

Yours,
Beginner
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Re: parsing an Excel formula with the re module

[vsoler]

On 5 ene, 20:05, Mensanator  wrote:
> On Jan 5, 12:35 pm, MRAB  wrote:
>
>
>
> > vsoler wrote:
> > > Hello,
>
> > > I am acessing an Excel file by means of Win 32 COM technology.
> > > For a given cell, I am able to read its formula. I want to make a map
> > > of how cells reference one another, how different sheets reference one
> > > another, how workbooks reference one another, etc.
>
> > > Hence, I need to parse Excel formulas. Can I do it by means only of re
> > > (regular expressions)?
>
> > > I know that for simple formulas such as "=3*A7+5" it is indeed
> > > possible. What about complex for formulas that include functions,
> > > sheet names and possibly other *.xls files?
>
> > > For example    "=Book1!A5+8" should be parsed into ["=","Book1", "!",
> > > "A5","+","8"]
>
> > > Can anybody help? Any suggestions?
>
> > Do you mean "how" or do you really mean "whether", ie, get a list of the
> > other cells that are referred to by a certain cell, for example,
> > "=3*A7+5" should give ["A7"] and "=Book1!A5+8" should give ["Book1!A5]
>
> Ok, although "Book1" would be the default name of a workbook, with
> default
> worksheets labeled "Sheet1". "Sheet2", etc.
>
> If I had a worksheet named "Sheety" that wanted to reference a cell on
> "Sheetx"
> OF THE SAME WORKBOOK, it would be =Sheet2!A7. If the reference was to
> a completely
> different workbook (say Book1 with worksheets labeled "Sheet1",
> "Sheet2") then
> the cell might have =[Book1]Sheet1!A7.
>
> And don't forget the $'s! You may see =[Book1]Sheet1!$A$7.

Yes, Mensanator, but...  what re should I use? I'm looking for the re
statement. No doubt you can help!

Thank you.
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Re: twenty years ago Guido created Python

[Steve Holden]

Phlip wrote:
> On Dec 31 2009, 2:06 pm, Steve Howell  wrote:
> 
>> Python is a truly awesome programming language.  Not only is Guido a
>> genius language designer, but he is also a great project leader.  What
>> an accomplishment.  Congratulations to everybody who has contributed
>> to Python in the last two decades!
> 
> The more languages you learn before getting to Smalltalk, the more
> awesome Smalltalk will be for you.
> 
After implementing SmallTalk I more or less gave up OO programming for
ten years, resuming it only after I met Python. SmallTalk didn't seem
that awesome to me.

Though for its time it was an incredible system, its insistence on a
SmallTalk-only VM environment seemed a little solipsistic.

regards
 Steve
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Re: parsing an Excel formula with the re module

[MRAB]

vsoler wrote:

On 5 ene, 19:35, MRAB  wrote:

vsoler wrote:

Hello,
I am acessing an Excel file by means of Win 32 COM technology.
For a given cell, I am able to read its formula. I want to make a map
of how cells reference one another, how different sheets reference one
another, how workbooks reference one another, etc.
Hence, I need to parse Excel formulas. Can I do it by means only of re
(regular expressions)?
I know that for simple formulas such as "=3*A7+5" it is indeed
possible. What about complex for formulas that include functions,
sheet names and possibly other *.xls files?
For example"=Book1!A5+8" should be parsed into ["=","Book1", "!",
"A5","+","8"]
Can anybody help? Any suggestions?

Do you mean "how" or do you really mean "whether", ie, get a list of the
other cells that are referred to by a certain cell, for example,
"=3*A7+5" should give ["A7"] and "=Book1!A5+8" should give ["Book1!A5"]?


I'd like to know how to do it, should it be possible.


Something like this should work:

references = re.findall(r"\b((?:\w+!)?[A-Za-z]+\d+)\b", formula)
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Re: Printing plain text with exact positioning on Windows

[Nobody]

On Tue, 05 Jan 2010 04:40:14 -0800, KvS wrote:

>> Did you mean borderless printing?
>> Every printer needs his margins, some more some less. Some printers have the
>> ability to do borderless printing but usualy they can do it only on special
>> or photo paper. So you can adjust the pdf as you wish, even with no margins,
>> and then try to find under printer options "borderless printing". That is
>> why I didn't understand :-)) it is a printer thing not pdf!
> 
> As much as possible "borderless", yes. Of course the printer will
> still apply some small margin, but that's ok. A margin of say <0.5 cm.
> is fine. So it's not a printer thing, I accept the (physical)
> limitations of the printer, but I want to avoid any extra margins due
> to software settings.

"Hardcopy" document formats such as PostScript and PDF use positions
relative to the edges of the page, not the margins.

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Re: Speeding up network access: threading?

[Steve Holden]

Jens Müller wrote:
> Hi and sorry for double posting - had mailer problems,
> 
>> Terry said "queue". not "list". Use the Queue class (it's thread-safe)
>> in the "Queue" module (assuming you're using Python 2.x; in Python 3.x
>> it's called the "queue" module).
> 
> Yes yes, I know. I use a queue to realize the thread pool queue, that
> works all right.
> 
> But each worker thread calculates a result and needs to make it
> avaialable to the application in the main thread again. Therefore, it
> appends its result to a common list. This seems works as well, but I was
> thinking of possible conflict situations that maybe could happen when
> two threads append their results to that same result list at the same
> moment.
> 
If you don't need to take anything off the list ever, just create a
separate thread that reads items from an output Queue and appends them
to the list.

If you *do* take them off, then use a Queue.

regards
 Steve
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Re: What is the best data structure for a very simple spreadsheet?

[vsoler]

On 3 ene, 22:40, mdipierro  wrote:
> Perhaps this can be useful:http://www.web2py.com/examples/spreadsheet
>
> The code is in a single file with not dependencies and it does not
> require web2py to 
> run:http://code.google.com/p/web2py/source/browse/gluon/contrib/spreadshe...
>
> Here is a sample controller that shows you how to embed the
> spreadsheet in web 
> page:http://code.google.com/p/web2py/source/browse/applications/examples/c...
>
> Massimo
>
> On Jan 3, 5:27 am, vsoler  wrote:
>
> > Hi,
>
> > Not sure this is the best group to post, but I cannot think of any
> > other.
>
> > My application would contain a limited set of "cells" represented by
> > the instances of a Cell class:
>
> > class Cell:
> > ...
>
> > A1=Cell(7)
> > A2=Cell(2*A1)
> > A3=Cell(3*A1+A2)
> > A4=Cell(A3*4)
>
> > Of course, A1 = 7, A2 = 14, A3 = 35 and A4 = 140
>
> > Now, I somehow want to be able to show a dependency tree
>
> > 1 level dependency trees
> >   A1: None
> >   A2: A1
> >   A3: A1, A2
> >   A4: A3
>
> > All levels dependency trees
>
> >   A1: None
> >   A2: A1
> >   A3: A1, A2
> >   A4: A3, A2, A1
>
> > Leaf + values dependency trees:
>
> >   A1: 7
> >   A2: A1=7, 2
> >   A3: 3, A1=7, 2
> >   A4: 3, A1=7, 2, 4
>
> > What I'd like to know is:
>
> > 1) what are, in your opinion, the basic elements of the Cell class?
> > 2) Do I need a parser to evaluate the formulas like “3*A1+A2”? Can you
> > recommend one library that already contains one?
> > 3) Do I need a tree data structure to represent my data? would the
> > tree be an attribute of the class instance?
>
> > I imagine a lot can be said on these questions. What I am looking for
> > is some hints that help me get out of where I am now.
>
> > Any help is highly appreciated.
>
> > Vicente Soler
>
>

There is something that I appreciate in this group, and it is the high
degree of knowledge of all the participants that are helping with
their answers.

After studying your suggestions, I'll come back to you.

Thank you very much.

Vicente Soler
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Re: fsync() doesn't work as advertised?

[Nobody]

On Mon, 04 Jan 2010 08:09:56 -0800, Brian D wrote:

> If I'm running a process in a loop that runs for a long time, I
> occasionally would like to look at a log to see how it's going.
> 
> I know about the logging module, and may yet decide to use that.
> 
> Still, I'm troubled by how fsync() doesn't seem to work as advertised:
> 
> http://docs.python.org/library/os.html
> 
> "If you’re starting with a Python file object f, first do f.flush(),
> and then do os.fsync(f.fileno())"

The .flush() method (and the C fflush() function) causes the
contents of application buffers to be sent to the OS, which basically
copies the data into the OS-level buffers.

fsync() causes the OS-level buffers to be written to the physical drive.

File operations normally use the OS-level buffers; e.g. if one process
write()s to a file and another process read()s it, the latter will see
what the former has written regardless of whether the data has been
written to the drive.

The main reason for using fsync() is to prevent important data from being
lost in the event of an unexpected reboot or power-cycle (an expected
reboot via the "shutdown" or "halt" commands will flush all OS-level
buffers to the drive first). Other than that, fsync() is almost invisible
(I say "almost", as there are mechanisms to bypass the OS-level buffers,
e.g. the O_DIRECT open() flag).

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Re: parsing an Excel formula with the re module

[Mensanator]

On Jan 5, 12:35 pm, MRAB  wrote:
> vsoler wrote:
> > Hello,
>
> > I am acessing an Excel file by means of Win 32 COM technology.
> > For a given cell, I am able to read its formula. I want to make a map
> > of how cells reference one another, how different sheets reference one
> > another, how workbooks reference one another, etc.
>
> > Hence, I need to parse Excel formulas. Can I do it by means only of re
> > (regular expressions)?
>
> > I know that for simple formulas such as "=3*A7+5" it is indeed
> > possible. What about complex for formulas that include functions,
> > sheet names and possibly other *.xls files?
>
> > For example    "=Book1!A5+8" should be parsed into ["=","Book1", "!",
> > "A5","+","8"]
>
> > Can anybody help? Any suggestions?
>
> Do you mean "how" or do you really mean "whether", ie, get a list of the
> other cells that are referred to by a certain cell, for example,
> "=3*A7+5" should give ["A7"] and "=Book1!A5+8" should give ["Book1!A5]

Ok, although "Book1" would be the default name of a workbook, with
default
worksheets labeled "Sheet1". "Sheet2", etc.

If I had a worksheet named "Sheety" that wanted to reference a cell on
"Sheetx"
OF THE SAME WORKBOOK, it would be =Sheet2!A7. If the reference was to
a completely
different workbook (say Book1 with worksheets labeled "Sheet1",
"Sheet2") then
the cell might have =[Book1]Sheet1!A7.

And don't forget the $'s! You may see =[Book1]Sheet1!$A$7.
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Re: parsing an Excel formula with the re module

[John Posner]

On Tue, 05 Jan 2010 13:12:00 -0500, vsoler  wrote:


Hello,

I am acessing an Excel file by means of Win 32 COM technology.
For a given cell, I am able to read its formula. I want to make a map
of how cells reference one another, how different sheets reference one
another, how workbooks reference one another, etc.

Hence, I need to parse Excel formulas. Can I do it by means only of re
(regular expressions)?

I know that for simple formulas such as "=3*A7+5" it is indeed
possible. What about complex for formulas that include functions,
sheet names and possibly other *.xls files?

For example"=Book1!A5+8" should be parsed into ["=","Book1", "!",
"A5","+","8"]

Can anybody help? Any suggestions?


It seems like you want to recreate data structures that Excel, itself,  
must maintain in order to recalculate cells in the correct order. As long  
as you're using COM, you might be able to tap into those data structures.  
My 15-year-old (!) "Using Excel Visual Basic for Applications" book wasn't  
any help. :-( After a short Google session, I came up with one possible  
lead: http://www.decisionmodels.com/


Good luck!
John
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Re: parsing an Excel formula with the re module

[vsoler]

On 5 ene, 19:35, MRAB  wrote:
> vsoler wrote:
> > Hello,
>
> > I am acessing an Excel file by means of Win 32 COM technology.
> > For a given cell, I am able to read its formula. I want to make a map
> > of how cells reference one another, how different sheets reference one
> > another, how workbooks reference one another, etc.
>
> > Hence, I need to parse Excel formulas. Can I do it by means only of re
> > (regular expressions)?
>
> > I know that for simple formulas such as "=3*A7+5" it is indeed
> > possible. What about complex for formulas that include functions,
> > sheet names and possibly other *.xls files?
>
> > For example    "=Book1!A5+8" should be parsed into ["=","Book1", "!",
> > "A5","+","8"]
>
> > Can anybody help? Any suggestions?
>
> Do you mean "how" or do you really mean "whether", ie, get a list of the
> other cells that are referred to by a certain cell, for example,
> "=3*A7+5" should give ["A7"] and "=Book1!A5+8" should give ["Book1!A5"]?

I'd like to know how to do it, should it be possible.

Vicente
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Re: twenty years ago Guido created Python

[Phlip]

On Dec 31 2009, 2:06 pm, Steve Howell  wrote:

> Python is a truly awesome programming language.  Not only is Guido a
> genius language designer, but he is also a great project leader.  What
> an accomplishment.  Congratulations to everybody who has contributed
> to Python in the last two decades!

The more languages you learn before getting to Smalltalk, the more
awesome Smalltalk will be for you.

--
  Phlip
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Re: IOError - cannot create file (linux daemon-invoked script)

[Nobody]

On Mon, 04 Jan 2010 21:30:31 -0800, cassiope wrote:

> One more tidbit observed: my last note, that it works when using
> seteuid/setegid?
> Well - that only applies if the daemon is running under strace (!).
> It fails
> if started directly by root, or if the strace session has ended,
> leaving the
> main body of the daemon running in its normal headless manner.
> 
> I wonder if running under "strace -f" - might setegid/seteuid be
> prevented from
> having their normal effect?

Possibly. The ptrace() syscall on which strace depends will fail if you
try to trace a "privileged" process and you aren't root, so it's possible
that a ptrace()d process will refuse to become privileged.

Here, "privileged" includes a process which has changed any of its UIDs or
GIDs (this prevents a normal user from tracing, killing, etc an otherwise
privileged process which has switched to the user's UID for the time being).

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Re: Speeding up network access: threading?

[Jens Müller]

Hi and sorry for double posting - had mailer problems,


Terry said "queue". not "list". Use the Queue class (it's thread-safe)
in the "Queue" module (assuming you're using Python 2.x; in Python 3.x
it's called the "queue" module).


Yes yes, I know. I use a queue to realize the thread pool queue, that works 
all right.


But each worker thread calculates a result and needs to make it avaialable 
to the application in the main thread again. Therefore, it appends its 
result to a common list. This seems works as well, but I was thinking of 
possible conflict situations that maybe could happen when two threads append 
their results to that same result list at the same moment.


Regards,
Jens 


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Re: parsing an Excel formula with the re module

[MRAB]

vsoler wrote:

Hello,

I am acessing an Excel file by means of Win 32 COM technology.
For a given cell, I am able to read its formula. I want to make a map
of how cells reference one another, how different sheets reference one
another, how workbooks reference one another, etc.

Hence, I need to parse Excel formulas. Can I do it by means only of re
(regular expressions)?

I know that for simple formulas such as "=3*A7+5" it is indeed
possible. What about complex for formulas that include functions,
sheet names and possibly other *.xls files?

For example"=Book1!A5+8" should be parsed into ["=","Book1", "!",
"A5","+","8"]

Can anybody help? Any suggestions?


Do you mean "how" or do you really mean "whether", ie, get a list of the
other cells that are referred to by a certain cell, for example,
"=3*A7+5" should give ["A7"] and "=Book1!A5+8" should give ["Book1!A5"]?
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it gets worse (was: How do you configure IDLE on a Mac...)

[Mensanator]

On Jan 5, 12:32 am, Ned Deily  wrote:
> In article
> <0d70cb54-3d77-4176-b621-e764ecf61...@26g2000yqo.googlegroups.com>,
>
>
>
>
>
>  Mensanator  wrote:
> > I assume I've been using the IDLE from macports. From the command
> > prompt I've
> > been typing "idle". This launches a "shell" window which appears to
> > have an X11
> > parent application for which there are no "preferences" applicable to
> > fonts.
>
> > However, if I use the quick launcher from the python.org, I get a
> > "shell" whose
> > parent is named "IDLE"! And that one has a completely different
> > preferences,
> > one similar the the Windows Configure which allows me to set the font!
>
> > Now, if I close this shell and start IDLE from the command line again,
> > I still
> > get a "shell" with an X11 parent, but, lo and behold, the font has
> > changed to
> > what I had previously set with the IDLE parent.
>
> > Course, I can't import gmpy, cause the python.org version can't
> > compile it, so I
> > still have to use the macports install of 3.1, but that's ok, once I
> > use
> > the IDLE application to set the preferences, I can switch back to the
> > X11 version and the preferences will follow.
>
> The prefs follow because all versions of IDLE use the same (unversioned)
> directory for configuration files, ~/.idlerc/.  In particular, the
> configuration file ~/.idlerc/config-main.cfg contains, among other
> things, any changes to the default font.  So, if you're successful at
> changing it in one version of IDLE, it will likely affect all versions
> you have.  Note the file is a simple ini format:
>
> [EditorWindow]
> font = monaco
>
> so you can edit it by hand.

Good to know. But, as the subject says...

>
> BTW, the python.org IDLEs and the Apple-supplied IDLEs use the
> system-supplied Aqua (aka Quartz) Tk not the X11 one that MacPorts
> builds by default.  The MacPorts Tk port does have a "quartz" variant
> but that doesn't yet work in 64-bit mode.

So, for all practical purposes, the macports install is broken also.

IDLE simply does not work in an X11 window (you think someone would
have noticed that). The missing preferences is just the beginning.
Apparently NONE of the menu item shortcuts work.

For example, the Cut, Copy, Paste shortcuts are given as Command-X,
Command-C and Command-V. But that doesn't work in an X11 window,
apperently only in an Aqua Tk (parent application appears as IDLE).

Of course, I can do Control-X, Control-C and Control-V to do Cut,
Copy and Paste. Don't know if this works for all shortcuts, but
I suppose I could just pick them from the menu (and I can bang
my head against the wall while I'm at it).

What do you think, suppose I copy the gmpy built with the macports
install over to the directory where the python.org version is? Would
it
import? If that'll work, I can switch back to using the python.org
install and use it's version of IDLE. I certainly won't be needing
distutils once I have a working version of gmpy.

>
> --
>  Ned Deily,
>  n...@acm.org- Hide quoted text -
>
> - Show quoted text -

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Re: Printing plain text with exact positioning on Windows

[KvS]

On Jan 5, 12:56 pm, Chris Gonnerman
 wrote:
> KvS wrote:
> > ... can I adjust the options normally appearing in
> > the Printing Dialog through Python?
>
> Yes, if you use my method or my module, as I gave in my previous post.  
> If you use Adobe Reader to print, I'm not sure how to automate the print
> settings.

Sorry, one more. I completely forgot it's not exactly plain text, but
occasionally also a limited number of non-ASCII characters (accents in
names etc.). Would this be possible through your method?
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parsing an Excel formula with the re module

[vsoler]

Hello,

I am acessing an Excel file by means of Win 32 COM technology.
For a given cell, I am able to read its formula. I want to make a map
of how cells reference one another, how different sheets reference one
another, how workbooks reference one another, etc.

Hence, I need to parse Excel formulas. Can I do it by means only of re
(regular expressions)?

I know that for simple formulas such as "=3*A7+5" it is indeed
possible. What about complex for formulas that include functions,
sheet names and possibly other *.xls files?

For example"=Book1!A5+8" should be parsed into ["=","Book1", "!",
"A5","+","8"]

Can anybody help? Any suggestions?

Vicente Soler
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Re: Dynamic text color

[John Posner]

On Tue, 05 Jan 2010 10:31:09 -0500, Dave McCormick   
wrote:



... But this is what I have so far.
##
file = 'red.txt'
file = open("red.txt","r")
rList = file.readlines()
file.close()
redList = str(rList).split()


Dave, you're doing exactly the right thing: gradually expanding your  
program, to provide more functionality and to learn more about the  
available programming tools. It's also very good that you take care to  
close() the file after processing it. Now for the bad news ...


1. Don't use "file" as a variable name -- it's a built-in object type.  
(Some people don't like the fact that Python allows you to redefine such  
"reserved words".)


2. It's probably not the best idea to use a single variable (you use  
"file") to do double-duty: to hold the name of a file, and to hold the  
open-file object returned by the open() function. It's perfectly legal,  
but it hides information that might be useful when you're debugging a  
program. This is better:


  fname = 'red.txt'
  inpf = open(fname, "r")

3. It might be better to use read() rather than readlines() to process the  
"red.txt" file. It depends on what that file is supposed to contain. For  
example, if you expect "red.txt" to contain exactly one line, which has  
one or more words, you can process the open-file object like this:


  file_contents = inpf.read()
  redList = file_contents.split()

   ... or ...

  redList = inpf.read().split()

It's certainly a mistake to use the expression "str(rList).split()". Using  
str() to convert the list "rList" into a string creates a mess that  
includes square-bracket characters. Did this actually work for you?


Best,
John

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Re: Exception as the primary error handling mechanism?

[Steve Holden]

D'Arcy J.M. Cain wrote:
> On 05 Jan 2010 14:02:50 GMT
> Steven D'Aprano  wrote:
>> shouldn't use assert for validating user data except for quick-and-dirty 
>> scripts you intend to use once and throw away.
> 
> A mythcial beast that has yet to be spotted in the wild.
> 
Not true (he wrote, picking nits). Such programs are written all the
time. The fact that they invariably get used more often than intended
doesn't negate the intentions of the author. ;-)

regards
 Steve
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Re: Speeding up network access: threading?

[Antoine Pitrou]

Le Tue, 05 Jan 2010 15:04:56 +0100, Jens Müller a écrit :
> 
> Is a list thrad-safe or do I need to lock when adding the results of my
> worker threads to a list? The order of the elements in the list does not
> matter.

The built-in list type is thread-safe, but is doesn't provide the waiting 
features that queue.Queue provides.

Regards

Antoine.

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Re: Exception as the primary error handling mechanism?

[Lie Ryan]

On 1/6/2010 1:48 AM, r0g wrote:

Steven D'Aprano wrote:

On Tue, 05 Jan 2010 13:06:20 +, r0g wrote:

If
that's the case how can you expect it to validate anything at all in
production?


The asserts still operate so long as you don't use the -O switch.


Do you mean for debugging in situ or something? Could you
maybe give me an example scenario to illustrate your point?



There are at least two sorts of validation that you will generally need
to perform: validating user data, and validating your program logic.





Cool, that's what I thought i.e. you can't rely on asserts being there
so don't use them for anything critical but it's still a good idea to
use them for logic/consistency checking in production code as, should
you be running your production code unoptimised, it might catch
something you'd otherwise miss.


Steven described the traditional approach to using assertions; another 
approach to when to use assertion is the one inspired by 
Design-by-Contract paradigm. DbC extends the traditional approach by 
focusing on writing a contract (instead of writing assertions) and 
generating assertions[1] to validate the contract. Just like assertions, 
these contracts are meant to be removed in production releases.


In Design-by-Contract, only codes that interacts with the outer-world 
(e.g. getting user/file/network input, etc) need to do any sort of 
validations. Codes that doesn't interact directly with outside world 
only need to have a "contract" and simplified by *not* needing argument 
checking, since the function relies on the caller obeying the 
contract[2] and never calling it with an invalid input.


DbC uses assertions[1] spuriously, unlike the traditional approach which 
is much more conservative when using assertions.


[1] or explicit language support which is just syntax sugar for assertions
[2] of course, on a debug release, the contract validation code will 
still be enforced to catch logic/consistency bugs that causes the violation

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Re: Speeding up network access: threading?

[MRAB]

Jens Müller wrote:

Hello,


The fairly obvious thing to do is use a queue.queue for tasks and another
for results and a pool of threads that read, fetch, and write.


Thanks, indeed.

Is a list thrad-safe or do I need to lock when adding the results of my
worker threads to a list? The order of the elements in the list does not
matter.


Terry said "queue". not "list". Use the Queue class (it's thread-safe)
in the "Queue" module (assuming you're using Python 2.x; in Python 3.x
it's called the "queue" module).
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Re: Where's a DOM builder that uses the Builder Pattern to ... build DOMs?

[Phlip]

On Jan 5, 12:16 am, Stefan Behnel  wrote:

> Note that there are tons of ways to generate HTML with Python.

Forgot to note - I'm generating schematic XML, and I'm trying to find
a way better than the Django template I started with!
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Re: A null program - what is it doing?

[John Posner]

No doubt a dumb question from a noob:

The following program (a cut down version of some test code) uses no 
CPU, and does not terminate:


import sys
from PyQt4.QtCore import *

if __name__=="__main__":
app = QCoreApplication(sys.argv)
sys.exit(app.exec_())

What is the program doing?  What is the correct way to terminate the 
execution?




Are you trying to understand QCoreApplication()? I can't help you there, 
since I've never used it. If you're just trying to get started with 
PyQt, use QApplication() instead:


import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *

if __name__=="__main__":
   app = QApplication(sys.argv)
   window = QLabel("I'm a PyQt window")
   window.show()
   sys.exit(app.exec_())

To terminate execution, just close the window by clicking the "X" in the 
window banner.


HTH,
John

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Re: Printing plain text with exact positioning on Windows

[KvS]

On Jan 5, 12:56 pm, Chris Gonnerman
 wrote:
> KvS wrote:
> > ... can I adjust the options normally appearing in
> > the Printing Dialog through Python?
>
> Yes, if you use my method or my module, as I gave in my previous post.  
> If you use Adobe Reader to print, I'm not sure how to automate the print
> settings.

Ok, actually I quite like being able to print straightforward through
your code, i.e. without any extra modules installed. I understand that
sending text to the printer is in principle as simple as

dc.TextOut(scale_factor * 72,
-1 * scale_factor * 72,
"Testing...")

I didn't see you do anything with adjusting margins in the code. Does
that mean that if I would e.g. do

dc.TextOut(0,
0,
"Testing...")

the printout would appear in the upper left corner of the paper, as
close to the edges as the printer is capable of? (Sorry, but I only
have Ubuntu available at the moment, no Windows).
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Re: Printing plain text with exact positioning on Windows

[KvS]

On Jan 5, 12:56 pm, Chris Gonnerman
 wrote:
> KvS wrote:
> > ... can I adjust the options normally appearing in
> > the Printing Dialog through Python?
>
> Yes, if you use my method or my module, as I gave in my previous post.  
> If you use Adobe Reader to print, I'm not sure how to automate the print
> settings.

Thanks Chris, I'll go on and have a look.
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Re: Speeding up network access: threading?

[Jens Müller]

Hello,

The fairly obvious thing to do is use a queue.queue for tasks and another 
for results and a pool of threads that read, fetch, and write.


Thanks, indeed.

Is a list thrad-safe or do I need to lock when adding the results of my 
worker threads to a list? The order of the elements in the list does not 
matter.


Jens 


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Re: Speeding up network access: threading?

[Jens Müller]

Hello,


The fairly obvious thing to do is use a queue.queue for tasks and another
for results and a pool of threads that read, fetch, and write.


Thanks, indeed.

Is a list thrad-safe or do I need to lock when adding the results of my
worker threads to a list? The order of the elements in the list does not
matter.

Jens

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Re: embedded python on mac - linking problem

[Benjamin Kaplan]

On Tue, Jan 5, 2010 at 7:33 AM, Krzysztof Kobus  wrote:
> Hi,
>
> I have a problem with linking python module with my application on mac in 
> order to make the module available in "embedded python".
>
> My python module is contained in  j3kmodule.cxx file and module 
> initialization function is exported in j3kmodule.h
>
> j3kmodule.h:
> 
> PyMODINIT_FUNC PyInit_j3k(void);
>
>
> j3kmodule.cxx:
> --
> PyMODINIT_FUNC
> PyInit_j3k(void)
>  {
>  PyObject *m = NULL;
>
>  if ((m = PyModule_Create(&j3k_module)) == NULL)
>    return NULL;
>
>  return m;
>  }
>
>
> Then in my application in KkPython.cxx file I have:
>
> KkPython.cxx:
> -
>
> #include "j3kmodule.h"
>
> /* Add a builtin module, before Py_Initialize */
> PyImport_AppendInittab("j3k", PyInit_j3k);
>
>
> I link my application with the module and get following linking error on mac 
> although on open suse linux exactly the same procedure works fine:
>
> g++ -headerpad_max_install_names -o 
> ../../bin/render.app/Contents/MacOS/render main.o KkPython.o -lkkbase 
> -L/Users/kk/dev/J3K/trunk/j3ksrc/examples/render/../../lib/ 
> -lQtSolutions_PropertyBrowser-2.5 -lpython3.1 
> /Users/kk/dev/J3K/trunk/j3ksrc/python/modules/build/lib.macosx-10.3-i386-3.1/j3k.so
>  -framework OpenGL -framework AGL
> ld: warning in 
> /Users/kk/dev/J3K/trunk/j3ksrc/python/modules/build/lib.macosx-10.3-i386-3.1/j3k.so,
>  file is not of required architecture
> Undefined symbols:
>  "_PyInit_j3k", referenced from:
>      _PyInit_j3k$non_lazy_ptr in KkPython.o
> ld: symbol(s) not found
> collect2: ld returned 1 exit status
> make: *** [../../bin/render.app/Contents/MacOS/render] Error 1
>
>
> I appreciate any hints,
>
> best greetings,
>
> Krzysztof Kobus
>

Well, it seems that one of your files is a different architecture than
the others. Based on the location, I'd say it's i386 while the rest of
it would be PowerPC. You can cross-compile but you can't link an i386
library to a PowerPC library.
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Re: Exception as the primary error handling mechanism?

[Dave Angel]

r0g wrote:

Dave Angel wrote:
  

r0g wrote:




Maybe, although I recently learned on here that one can't rely on assert
 statements in production code, their intended use is to aid debugging
and testing really.

  
  

Hopefully, what you learned is that you can't use assert() in production
code to validate user data.  It's fine to use it to validate program
logic, because that shouldn't still need testing in production.



DaveA





Well maybe I didn't quite get it then, could you explain a bit further?

My understanding was that asserts aren't executed at all if python is
started with the -O or -OO option, or run through an optimizer. If
that's the case how can you expect it to validate anything at all in
production? Do you mean for debugging in situ or something? Could you
maybe give me an example scenario to illustrate your point?

Cheers,

Roger.

  
You understand the -O and -OO options fine.  But the point is that you 
should not use assert() for anything that will be properly debugged 
before going to the user.  You use if statements, and throw's to catch 
the error, and print to stderr, or GUI dialog boxes, or whatever 
mechanism you use to tell your user.  But those errors are ones caused 
by his data, not by your buggy code.  And the message tells him what's 
wrong with his data, not that you encountered a negative value for some 
low level function.


I agree with Steve's pessimistic view of the state of most released 
software.  But if you view a particular internal check as useful for 
production, then it should be coded in another mechanism, not in 
assert.  Go ahead and write one, with a UI that's appropriate for your 
particular application.  But it should do a lot more than assert does, 
including telling the user your contact information to call for support.


   def production_assert(expression, message):
if  not expression:
  dialog_box("Serious internal bug, 
call  NNN-NNN- immediately", message)



For an overly simplified example showing a user validation, and an assert :

import sys
def main():
   try:
   text = raw_input("Enter your age, between 1 and 22 ")
   age = int(text)
   except  ValueError, e:
   age = -1
   if not 1 <= age <= 22: #not an assert
   print "Age must be between 1 and 22"
   print "Run program again"
   sys.exit(2)
   grade = calc_grade(age)
   print "Your grade is probably", grade

table = [0, 0, 0, 0, 0, "K", "First", "2nd", 3]
def calc_grade(age):
   """ calculate a probable grade value, given an
   i2nteger age between 1 and 22, inclusive
   """
   assert(1 <= age <= len(table))
   grade = table[age]#assume I have a fixed-length table for this
   return grade

main()

Note a few things.  One I have a bug, in that the table isn't as big as 
the limit I'm checking for.  With defensive coding, I'd have another 
assert for that, or even have the table size be available as a global 
constant (all uppers) so that everyone's in synch on the upper limit.  
But in any case, the test suite would be checking to make sure the code 
worked for 1, for 22, for a couple of values in between, and that a 
proper error response happened when a non-integer was entered, or one 
outside of the range.  That all happens in separate code, not something 
in this file.  And the test suite is run after every change to the 
sources, and certainly before release to production.


Next, see the docstring.  It establishes a precondition for the 
function.  Since the function is called only by me (not the user), any 
preconditions can be checked with an assert.  An assert without a 
supporting comment (or docstring) is almost worthless.


And finally, notice that I check the user's input *before* passing it on 
to any uncontrolled code.  So any asserts after that cannot fire, unless 
I have a bug which was not caught during testing.


All opinions my own, of course.

DaveA

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Re: Dynamic text color

[Dave McCormick]

John Posner wrote:
On Fri, 01 Jan 2010 21:01:04 -0500, Cousin Stanley 
 wrote:





I was not familiar with the re.finditer method
for searching strings ...


Stanley and Dave --

So far, we've just been using finditer() to perform standard-string 
searches (e.g. on the word "red"). Since Dave now wants to color 
multiple words the same color (e.g. the words in redList), we can use 
a single regular-expression search to locate *all* the words in a 
list. This eliminates the need to use a "for" loop to handle the list. 
Here's what I mean:


 >>> import re
 >>> s = "it is neither red nor crimson, but scarlet, you see"

## individual searches

 >>> [matchobj.span() for matchobj in re.finditer("red", s)]
 [(14, 17)]
 >>> [matchobj.span() for matchobj in re.finditer("crimson", s)]
 [(22, 29)]
 >>> [matchobj.span() for matchobj in re.finditer("scarlet", s)]
 [(35, 42)]

## one "swell foop"

 >>> redList = "red crimson scarlet".split()
 >>> redList_regexp = "|".join(redList)
 >>> redList_regexp
 'red|crimson|scarlet'
 >>> [matchobj.span() for matchobj in re.finditer(redList_regexp, s)]
 [(14, 17), (22, 29), (35, 42)]

-John

Thanks again John,
This is fun!!!
I made a "red.text" file to hold the "red words", they are separated by 
a space in the file.
Still need to add the extra parameter "color" someplace. But this is 
what I have so far.

##
file = 'red.txt'
file = open("red.txt","r")
rList = file.readlines()
file.close()
redList = str(rList).split()
blueList = "blue ball".split()
greenList = "green grass".split()
def get_complete_text(event):
   complete_text = Tbox.get("1.0", END)
   Tbox.tag_remove("red", "1.0", END)
   Tbox.tag_remove("blue", "1.0", END)
   Tbox.tag_remove("green", "1.0", END)
RED
   redList_regexp = "|".join(redList)
   for matchobj in re.finditer(redList_regexp, complete_text):
   start,end = matchobj.span()
   Tbox.tag_add("red", "1.0 + %d chars" % start,"1.0 + %d chars" % end)
   Tbox.tag_config("red", foreground="red")
BLUE###
   blueList_regexp = "|".join(blueList)
   for matchobj in re.finditer(blueList_regexp, complete_text):
   start,end = matchobj.span()
   Tbox.tag_add("blue", "1.0 + %d chars" % start,"1.0 + %d chars" % 
end)

   Tbox.tag_config("blue", foreground="blue")
GREEN###
   greenList_regexp = "|".join(greenList)
   for matchobj in re.finditer(greenList_regexp, complete_text):
   start,end = matchobj.span()
   Tbox.tag_add("green", "1.0 + %d chars" % start,"1.0 + %d chars" 
% end)

   Tbox.tag_config("green", foreground="green")
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Re: ctypes: How to call unexported functions in a dll

[Thomas Heller]

Am 05.01.2010 12:19, schrieb Coert Klaver (DT):
> Hi,
> 
> I am using ctypes in python 3 on a WXP machine
> 
> Loading a dll and using its exported functions works fine.
> 
> Now I want to use a function in the dll that is not exported.
> 
> In C this can be done by just casting the address in the dll of that
> function to an apropriate function pointer and call it (you need to be
> sure about the address). Can a similar thing be done directly with
> ctypes?
> 
> A work around I see is writing in wrapper dll in c that loads the main
> dll, exports a function that calls the unexported function in the main
> dll, but I don't find that an elegant solution.

No need for a workaround.

One solution is to first create a prototype for the function by calling 
WINFUNCTYPE
or CFUNCTYPE, depending on the calling convention: stdcall or cdecl, then call 
the
prototype with the address of the dll function which will return a Python 
callable.
Demonstrated by the following script using GetProcAddress to get the address of
the GetModuleHandleA win32 api function:

>>> from ctypes import *
>>> dll = windll.kernel32
>>> addr = dll.GetProcAddress(dll._handle, "GetModuleHandleA")
>>> print hex(addr)
0x7c80b741
>>> proto = WINFUNCTYPE(c_int, c_char_p)
>>> func = proto(addr)
>>> func

>>> func(None)
486539264
>>> hex(func(None))
'0x1d00'
>>> hex(func("python24.dll"))
'0x1e00'
>>> hex(func("python.exe"))
'0x1d00'
>>>

Thomas
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Re: Exception as the primary error handling mechanism?

[r0g]

Steven D'Aprano wrote:
> On Tue, 05 Jan 2010 13:06:20 +, r0g wrote:

>> Well maybe I didn't quite get it then, could you explain a bit further?
>>
>> My understanding was that asserts aren't executed at all if python is
>> started with the -O or -OO option, 
> 
> Correct.
> 
> 
>> or run through an optimizer. 
> 
> I don't know what you mean by that.


I've never used them but I heard there are optimizers for python
(psycho?). I assumed these would do everythin -O does and more,
including losing the asserts.



> 
>> If
>> that's the case how can you expect it to validate anything at all in
>> production? 
> 
> The asserts still operate so long as you don't use the -O switch.
> 
>> Do you mean for debugging in situ or something? Could you
>> maybe give me an example scenario to illustrate your point?
> 
> 
> There are at least two sorts of validation that you will generally need 
> to perform: validating user data, and validating your program logic.
> 



Cool, that's what I thought i.e. you can't rely on asserts being there
so don't use them for anything critical but it's still a good idea to
use them for logic/consistency checking in production code as, should
you be running your production code unoptimised, it might catch
something you'd otherwise miss.

Thanks for responding is such detail :)

Roger.
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Re: twenty years ago Guido created Python

[n00m]

Stick your English into your ass
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