How to build an application in Django which will handle Multiple servers accross network

[Anurag (anu) Agarwal]

Hi All,

I want to build an application for one of my client which has
following features

1. Client has some driver software which can be installed on Windows
and Linux based systems. This driver software is fetching some
operating system details using kernel level programming.
2. Now a new web based application is required to moniter these
servers remotly. This application will talk to these servers and get
the data (not sure how data will be fetched from driver software) then
show it on UI.
3. The web based application will be used internally in the network to
moniter servers in that network only.
4. Web based application will be a real time application with a
Database.
5. Technology I am thingking for web based application is Django and
Python as this web application can also be installed on Windows or
Linux based OS.
6. Also please suggest which third party tool for chatrs and graphs I
should use with Django (open source + paid)

If you guys can help me in desiging a very high level Architecture of
this application.

Thanks for reading so long. Please help me in this. If I am not clear
on something then please write back.

Thanks & Regards,
Anurag
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Re: Composition instead of inheritance

[John Nagle]

On 4/28/2011 3:35 PM, Carl Banks wrote:

On Thursday, April 28, 2011 10:15:02 AM UTC-7, Ethan Furman wrote:

For anybody interested in composition instead of multiple
inheritance, I have posted this recipe on ActiveState (for python
2.6/7, not 3.x):

http://code.activestate.com/recipes/577658-composition-of-classes-instead-of-multiple-inherit/




Comments welcome!


That's not what we mean by composition.  Composition is when one
object calls upon another object that it owns to implement some of
its behavior.  Often used to model a part/whole relationship, hence
the name.


The distinction isn't that strong in Python, where an object
can't be part of another object.  Object fields are references, not
the objects themselves.

In C++, you really can have an object as a field of an enclosing
object.  The inner object's destructor will be called first.
Destructors and ownership tend not to be too important in Python,
because storage management is automatic.

John Nagle
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PyCon Australia 2011: cfp closing soon!

[Ryan Kelly]

Hi Everyone,


A reminder that the Call for Proposals for PyCon Australia 2011 will be
closing soon.  We've had some great proposals so far, but there is still
time left and program to fill.

PyCon Australia is Australia's only conference dedicated exclusively to
the Python programming language, and will be held at the Sydney Masonic
Center over the weekend of August 20 and 21. See below for more
information and updates on:

1. Call For Proposals
2. More Sponsors Announced

Please pass this message on to those you feel may be interested.



Call For Proposals
==

The deadline for proposal submission is the 2nd of May.
That's only a few days away!

We are looking for proposals for talks on all aspects of Python
programming from novice to advanced levels; applications and frameworks,
or how you have been involved in introducing Python into your
organisation. We're especially interested in short presentations that
will teach conference-goers something new and useful. Can you show
attendees how to use a module? Explore a Python language feature?
Package an application?

We welcome first-time speakers; we are a community conference and we
are eager to hear about your experience. If you have friends or
colleagues who have something valuable to contribute, twist their arms
to tell us about it! Please also forward this Call for Proposals to
anyone that you feel may be interested.

The earlier you submit your proposal, the more time we will have to
review and give you feedback before the program is finalised.

Speakers receive free registration for the conference, including a seat
at the conference dinner.  Don't miss out, submit your proposal today! 

http://pycon-au.org/cfp



More Sponsors Announced
===

We are delighted to announce that ComOps has joined as a Gold Sponsor.
Thank you to the following companies for their continuing support of
Python and for helping to make PyCon Australia 2011 a reality:


   Gold:  Google  
   Gold:  Microsoft   
   Gold:  ComOps  

   Silver:  Anchor
   Silver:  Enthought 
   Silver:  Python Software Foundation


Thanks also to Linux Australia, who provide the overarching legal and
organisational structure for PyCon Australia.




   Ryan Kelly
   PyCon Australia 2011





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Python RPM Package build error

[Wells, David J]

Hello List,

 

I am attempting to build an rpm from Python-3.1.3.tar.bz2 with the
included spec file from /Python-3.1.3/Misc/RPM/ and it fails with the
following error:

Does anyone have any ideas?

 

# rpmbuild -ba python-3.1.spec

 

mv: cannot stat `idle': No such file or directory

+ echo '#!/usr/bin/env python2.6'

+ echo 'import os, sys'

+ echo 'os.execvp("/usr/bin/python2.6", ["/usr/bin/python2.6",
"/usr/lib/python3.1/idlelib/idle.py"] + sys.argv[1:])'

+ echo 'print "Failed to exec Idle"'

+ echo 'sys.exit(1)'

+ chmod 755 /var/tmp/python2.6-3.1.3-root/usr/bin/idle2.6

+ cp -a Tools /var/tmp/python2.6-3.1.3-root/usr/lib64/python3.1

+ rm -f mainpkg.files

+ find /var/tmp/python2.6-3.1.3-root/usr/lib64/python3.1/lib-dynload -type
f

+ sed 's|^/var/tmp/python2.6-3.1.3-root|/|'

+ grep -v -e '_tkinter.so$'

error: Bad exit status from /var/tmp/rpm-tmp.7647 (%install)

 

/var/tmp/rpm-tmp.7647 include the following:

 

#  check to see if there are any straggling #! lines

find "$RPM_BUILD_ROOT" -type f | xargs egrep -n '^#!
*/usr/local/bin/python' \

  | grep ':1:#!' >/tmp/python-rpm-files.$$ || true

if [ -s /tmp/python-rpm-files.$$ ]

then

   echo '*'

   cat /tmp/python-rpm-files.$$

   cat <<@EOF

   *

 There are still files referencing /usr/local/bin/python in the

 install directory.  They are listed above.  Please fix the .spec

 file and try again.  If you are an end-user, you probably want

 to report this to jafo-r...@tummy.com as well.

   *

@EOF

   rm -f /tmp/python-rpm-files.$$

   exit 1

fi

rm -f /tmp/python-rpm-files.$$

 



#  CLEAN



 







/usr/lib/rpm/brp-compress 

/usr/lib/rpm/brp-strip 

/usr/lib/rpm/brp-strip-static-archive 

/usr/lib/rpm/brp-strip-comment-note

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Re: Composition instead of inheritance

[Ian Kelly]

On Thu, Apr 28, 2011 at 11:15 AM, Ethan Furman  wrote:
> For anybody interested in composition instead of multiple inheritance, I
> have posted this recipe on ActiveState (for python 2.6/7, not 3.x):
>
> http://code.activestate.com/recipes/577658-composition-of-classes-instead-of-multiple-inherit/
>
> Comments welcome!

On line 14, is it intentional that attributes whose values happen to
be false are not considered as conflicts?

On line 31, this code:

thing = getattr(thing, '__func__', None) or thing

could be simplified to this:

thing = getattr(thing, '__func__', thing)

Cheers,
Ian
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Re: use of index (beginner's question)

[Daniel Kluev]

On Thu, Apr 28, 2011 at 11:42 AM, Rusty Scalf  wrote:
> list1 = ['pig', 'horse', 'moose']
> list2 =  ['62327', '49123', '79115']
> n = 2
> s2 = "list" + `n`
> a = s2[list1.index('horse')]
> print a
>
>  -does not work

While advices above are indeed right way to go in your case, there is
a way to get variable by its name.

>>> list2 = ['62327', '49123', '79115']
>>> n = 2
>>> s2 = "list{0}".format(n)
>>> print s2
list2
>>> print locals()[s2]
['62327', '49123', '79115']
>>> print locals()[s2][0]
62327

But generally if you need to do that, you would be better with
re-design of your data/architecture.

-- 
With best regards,
Daniel Kluev
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Re: Composition instead of inheritance

[Ben Finney]

Dan Stromberg  writes:

> On Thu, Apr 28, 2011 at 3:35 PM, Carl Banks  wrote:
> > That's not what we mean by composition.  Composition is when one
> > object calls upon another object that it owns to implement some of
> > its behavior.  Often used to model a part/whole relationship, hence
> > the name.
>
> It's a pretty old idea, that seems to be getting revived in a big way
> all of a sudden. Perhaps the Java people just rediscovered it?

I think it's more that people keep re-discovering how irredeemably messy
multiple inheritance is, and finding that object composition is better
in most cases :-)

-- 
 \  “There's a fine line between fishing and standing on the shore |
  `\looking like an idiot.” —Steven Wright |
_o__)  |
Ben Finney
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Re: Composition instead of inheritance

[Dan Stromberg]

On Thu, Apr 28, 2011 at 3:35 PM, Carl Banks  wrote:
> On Thursday, April 28, 2011 10:15:02 AM UTC-7, Ethan Furman wrote:
>> For anybody interested in composition instead of multiple inheritance, I
>> have posted this recipe on ActiveState (for python 2.6/7, not 3.x):
>>
>> http://code.activestate.com/recipes/577658-composition-of-classes-instead-of-multiple-inherit/
>>
>> Comments welcome!
>
> That's not what we mean by composition.  Composition is when one object calls 
> upon another object that it owns to implement some of its behavior.  Often 
> used to model a part/whole relationship, hence the name.

It's a pretty old idea, that seems to be getting revived in a big way
all of a sudden.  Perhaps the Java people just rediscovered it?

In a Software Engineering class using Ada, the teacher called it
"Structural Inclusion", and of course it was an important concept in
Ada, because Ada had no inheritance.  This was in 1989-1990.
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Re: Composition instead of inheritance

[Ben Finney]

Steven D'Aprano  writes:

> On Thu, 28 Apr 2011 15:35:47 -0700, Carl Banks wrote:
>
> > That's not what we mean by composition. Composition is when one
> > object calls upon another object that it owns to implement some of
> > its behavior.
>
> I thought that was delegation. As in, when one object delegates some or 
> all of it's behaviour to another object:
>
> http://code.activestate.com/recipes/52295

The difference being that, with delegation, the object being called is
unrelated to this one. With composition, the object being called is not
wholly separate, but is instead an attribute on the current object.

The “another object that it owns” was, I presume, meant to communicate
this “an object which is an attribute of the current one” relationship.

> In mathematics, composition means to make a function by applying a 
> function to the output of another.

The term “composition” in the programming sense comes from OO design,
not functional nor mathematical terminology.

-- 
 \  “I don't like country music, but I don't mean to denigrate |
  `\  those who do. And for the people who like country music, |
_o__)denigrate means ‘put down’.” —Bob Newhart |
Ben Finney
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Re: Composition instead of inheritance

[Ben Finney]

Ethan Furman  writes:

> Carl Banks wrote:
> > That's not what we mean by composition. Composition is when one
> > object calls upon another object that it owns to implement some of
> > its behavior. Often used to model a part/whole relationship, hence
> > the name.
>
> Hmmm. Okay -- any ideas for a better term? Something that describes
> taking different source classes and fusing them into a new whole,
> possibly using single-inheritance... Frankenstein, maybe? ;)

(Remember that Frankenstein was not the monster, but the scientist.)

“Hybrid”?

-- 
 \  “If sharing a thing in no way diminishes it, it is not rightly |
  `\  owned if it is not shared.” —Augustine of Hippo (354–430 CE) |
_o__)  |
Ben Finney
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Re: Composition instead of inheritance

[James Mills]

On Fri, Apr 29, 2011 at 11:43 AM, Ethan Furman  wrote:
> Hmmm. Okay -- any ideas for a better term?  Something that describes taking
> different source classes and fusing them into a new whole, possibly using
> single-inheritance... Frankenstein, maybe?  ;)

I'd have to say that this is typical of MixIns

cheers
James

-- 
-- James Mills
--
-- "Problems are solved by method"
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Re: Composition instead of inheritance

[Steven D'Aprano]

On Thu, 28 Apr 2011 15:35:47 -0700, Carl Banks wrote:

> On Thursday, April 28, 2011 10:15:02 AM UTC-7, Ethan Furman wrote:
>> For anybody interested in composition instead of multiple inheritance,
>> I have posted this recipe on ActiveState (for python 2.6/7, not 3.x):
>> 
>> http://code.activestate.com/recipes/577658-composition-of-classes-
instead-of-multiple-inherit/
>> 
>> Comments welcome!
> 
> That's not what we mean by composition.  Composition is when one object
> calls upon another object that it owns to implement some of its
> behavior.

I thought that was delegation. As in, when one object delegates some or 
all of it's behaviour to another object:

http://code.activestate.com/recipes/52295


> Often used to model a part/whole relationship, hence the name.

In mathematics, composition means to make a function by applying a 
function to the output of another. E.g.:

f o g(x) is equivalent to f(g(x))

(Strictly speaking, the "o" in the f o g should be a little circle rather 
than lowercase "O".)



-- 
Steven
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Re: IDLE lost from Windows menu !

[Jayme Proni Filho]

I agree with MRAB because it is easy and fast solution.

---
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Skype: jaymeproni
Twitter: @jaymeproni
Phone: +55 - 17 - 3631 - 6576
Mobile: +55 - 17 - 9605 - 3560
e-Mail: jaymeproni at yahoo dot com dot br
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Re: IDLE lost from Windows menu !

[Alec Taylor]

Search for the following key in regedit: HKEY_CLASSES_ROOT\*\shell

Right click on “shell”, choose create new key.

Name it “Edit with IDLE"

Create a new key below that one and call it “command.”

Now double click on the (Default) value that you will find in the
right hand pane, and type in the following: python.exe %1

(or if you don't have it in your PATH, then put in the absolute python
directory, ie: C:\Python27\bin\python.exe)
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Re: Composition instead of inheritance

[MRAB]

On 29/04/2011 02:43, Ethan Furman wrote:

Carl Banks wrote:

That's not what we mean by composition. Composition is when one object

 > calls upon another object that it owns to implement some of its
behavior.
 > Often used to model a part/whole relationship, hence the name.

Hmmm. Okay -- any ideas for a better term? Something that describes
taking different source classes and fusing them into a new whole,
possibly using single-inheritance... Frankenstein, maybe? ;)


[snip]
Fusing/fusion? Compounding?
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Aborting Python from C code

[Chris Angelico]

In our sandboxed Python environment, I would like to be able to
trigger an abort of the currently-running Python script (from a signal
handler or another thread). Currently, I use PyErr_SetInterrupt()
which raises KeyboardInterrupt in the script; this works for the most
part, but can be bypassed with a script like:

while True:
try:
while True:
pass
except:
pass

I want to be able to administratively order Python to stop executing.
Is it possible to make KeyboardInterrupt non-catchable from Python?
Alternatively, can I use Py_AddPendingCall to do this? I'd rather not
use setjmp/longjmp if I can help it, as they seem a tad brutal, but
I'm thinking in terms of a call that, in effect, doesn't return.

Any ideas would be appreciated!

Chris Angelico
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回复: Re: Need your help

[1011_wxy]

Dear Thomas,JM,Chris Rebert:

I got it. Thank you very very very much.


Best Regards

2011-04-29



1011_wxy



发件人: Thomas Rachel 

发送时间: 2011-04-28 21:26
主 题: Re: Need your help
收件人: python-list@python.org



Am 28.04.2011 13:14, schrieb Chris Rebert: 

> import a, b, sys 
> def c(): 
>  orig_stdout = sys.stdout 
>  sys.stdout = open('my_log_file.log', 'w') 
>  a.a() 
>  b.b() 
>  sys.stdout.close() 
>  sys.stdout = orig_stdout 
> 
> 
> Someone may have written a with-statement context manager that 
> abstracts away the swapping. 

@contextlib.contextmanager 
def swap_stdout(target): 
 orig_stdout = sys.stdout 
 sys.stdout = target 
 try: 
 yield target 
 finally: 
 sys.stdout = orig_stdout 

In this case, I can use all kinds of files (open() files, StringIO  
objects etc.), and can re-use them if necessary, in order to  
prepend/append data. 

Closing can happen additionally, if the user wants. 


Thomas 
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Re: socket.gethostbyaddr() wrongly returning a DNS CNAME as the 'primary' hostname

[Dan Stromberg]

On Thu, Apr 28, 2011 at 1:18 PM, cjblaine  wrote:

> Thanks for the reply, Ned.
>
> Bummer for me.  Check this out:
>
> C code on Solaris 10 SPARC returns the following with nscd
> running (the Solaris Naming Services Caching Daemon, on by
> default):
>

I'm guessing the IP's PTR record is pointing to a CNAME rather than (one of)
the A record(s).
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Re: Composition instead of inheritance

[Ethan Furman]

Carl Banks wrote:

That's not what we mean by composition.  Composition is when one object

> calls upon another object that it owns to implement some of its behavior.
> Often used to model a part/whole relationship, hence the name.

Hmmm. Okay -- any ideas for a better term?  Something that describes 
taking different source classes and fusing them into a new whole, 
possibly using single-inheritance... Frankenstein, maybe?  ;)




The sorts of class that this decorator will work for are probably not

> the ones that are going to have problems cooperating in the first place.
> So you might as well just use inheritance; that way people trying to read
> the code will have a common, well-known Python construct rather than a
> custom decorator to understand.

From thread 'python and super' on Python-Dev:
Ricardo Kirkner wrote:
> I'll give you the example I came upon:
>
> I have a TestCase class, which inherits from both Django's TestCase
> and from some custom TestCases that act as mixin classes. So I have
> something like
>
> class MyTestCase(TestCase, Mixin1, Mixin2):
>...
>
> now django's TestCase class inherits from unittest2.TestCase, which we
> found was not calling super.

This is the type of situation the decorator was written for (although 
it's too simplistic to handle that exact case, as Ricardo goes on to say 
he has a setUp in each mixin that needs to be called -- it works fine 
though if you are not adding duplicate names).


~Ethan~
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Re: IDLE lost from Windows menu !

[Uncle Ben]

On Apr 28, 5:17 pm, Andrew Berg  wrote:
> On 2011.04.28 02:11 PM, Uncle Ben wrote:> It was suggested to me privately 
> that I search for
> > HKEY_CLASSES_ROOT\*\shell,
> > right_click on "shell",
> > create a new key called "EDIT with IDLE"
> > and another called "command python.exe %1"
>
> The key you're looking for is HKCR\Python.File\shell. Add a subkey
> called Edit with IDLE. Create a subkey in there called command. Inside
> HKCR\Python.File\shell\Edit with IDLE\command, modify the default value
> to "C:\Python32\pythonw.exe" "C:\Python32\Lib\idlelib\idle.pyw" -e "%1"
> (changing the paths if necessary). Do the same with
> HKCR\Python.NoConFile\shell to get the command for .pyw files.

Thanks to all for good help.  I finally got what I need by altering
the original advice (A.T.) slightly.

The key to edit was "HKCR/Applications/python.exe/shell",
the item is put into the menu in a sub-key labelled "Edit with IDLE",
and the command sub-sub-key that works for me is "idle.bat %1"

I will keep Andrew Berg's note and use it when I encounter .pyw
files.

Python's the ninth language I've had to learn. And I love it.

Uncle Ben

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Re: IDLE lost from Windows menu !

[Uncle Ben]

On Apr 28, 3:11 pm, Uncle Ben  wrote:
> On Apr 28, 12:28 pm, Uncle Ben  wrote:
>
> > I have lost the convenient feature that to edit a .py file I could
> > right-click on the file name and reach the menu item "Edit with IDLE".
>
> > The workaround is not hard, but it wouild be nice to get this feature
> > back.
>
> > It happened when I was mungeing around and downloaded Python 2.3.3 in
> > addition to Python 2.7.1, and got into trouble until I discovered
> > that I was involuntarily RUNNING the older version.  So I cleaned it
> > out, but still I have this aftermath.
>
> > Is there a Windows guru out there who can tell be how to add to the
> > right-click menu clicking on myfile.py?
>
> > Uncle Ben
>
> It was suggested to me privately that I search for
> HKEY_CLASSES_ROOT\*\shell,
> right_click on "shell",
> create a new key called "EDIT with IDLE"
> and another called "command python.exe %1"
>
> Problem:
>   Searching on the HKEY group as above yields no "shell".
>
> Did I not do it right, or is there another way?
>
> (I would think that that command would execute my file, not edit it.
> But maybe I will be surprised.)
>
> (I am running Windows 7, 64-bit.)
>
> Uncle Ben

Thanks to all for good help.  I finally got what I need by altering
the original advice (A.W.) slightly.

The key to edit was "HKCR/Applications/python.exe/shell",
the item is put into the menu in a sub-key labelled "Edit with IDLE",
and the command sub-sub-key that works for me is "idle.bat %1"

I will keep Andrew Berg's note and use it when I encounter .pyw files.

Python's the ninth language I've had to learn. And I love it.

Uncle Ben
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Re: [OT] VCS tools

[Daniel Kluev]

On Fri, Apr 29, 2011 at 8:50 AM, Ben Finney  wrote:
> Martin Schöön  writes:
>
> I seriously recommend anyone looking for a modern VCS to give Bazaar a
> decent trial. It's the one I've found newcomers learn most easily, and
> it's astoundingly flexible as one's needs with it grow.
>

When I was deciding what DVCS I should use for personal projects, Bzr
was first thing I tried. It was quite uncomfortable experience after
svn, esp. with branches and merges, working not the way I was
expecting it to.
Mercurial, on the contrary, did exactly what I was expecting it to,
and was overall very easy to learn.

-- 
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Daniel Kluev
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Re: [OT] VCS tools

[Tim Chase]

On 04/28/2011 04:50 PM, Ben Finney wrote:

This has been a pretty informative thread so far. Please keep it coming.
I am a hardware development guy and do very little software development.
I have been vaguely aware of tools for version control but inspired by
this thread I have started looking at Mercurial.


After my passionate Bazaar evangelism? :-)


I must say my takeaway from the thread was (1) check back in on 
Bazaar to see if the speed is better than I remember and (2) 
Fossil, wha? wow!


-tkc


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Re: Read-write lock for Python

[Ryan Kelly]

On Thu, 2011-04-28 at 07:02 -0700, Geoff Bache wrote:
> Hi all,
> 
> I currently find myself needing a Python read-write lock. I note that
> there is none in the standard library, but googling "python read-write
> lock" quickly produced 6 different competing examples, including two
> languishing patch proposals for the standard library.
> 
> I can always pick a random one and hope for the best, but I was hoping
> someone here might have a tip for one that has been used and debugged
> and is likely to work.

I wrote and have used the "SHLock" class in threading2 which should do
what you need.  Don't know about "likely to work" but if it doesn't, I'd
like to hear about it so I can fix it :-)

  `pip install threading2`


  Cheers,

Ryan


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Description: This is a digitally signed message part
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Re: Composition instead of inheritance

[Carl Banks]

On Thursday, April 28, 2011 10:15:02 AM UTC-7, Ethan Furman wrote:
> For anybody interested in composition instead of multiple inheritance, I 
> have posted this recipe on ActiveState (for python 2.6/7, not 3.x):
> 
> http://code.activestate.com/recipes/577658-composition-of-classes-instead-of-multiple-inherit/
> 
> Comments welcome!

That's not what we mean by composition.  Composition is when one object calls 
upon another object that it owns to implement some of its behavior.  Often used 
to model a part/whole relationship, hence the name.

The sorts of class that this decorator will work for are probably not the ones 
that are going to have problems cooperating in the first place.  So you might 
as well just use inheritance; that way people trying to read the code will have 
a common, well-known Python construct rather than a custom decorator to 
understand.

If you want to enforce no duplication of attributes you can do that, such as 
with this untested metaclass:

class MakeSureNoBasesHaveTheSameClassAttributesMetaclass(type):
def __new__(metatype,name,bases,dct):
u = collections.Counter()
for base in bases:
for key in base.__dict__.keys():
u[key] += 1
for key in dct.keys():
u[key] += 1
if any(u[key] > 1 for key in u.keys()):
raise TypeError("base classes and this class share some class 
attributes")
return type.__new__(metatype,name,bases,dct)
 

Carl Banks
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Re: NaN

[Grant Edwards]

On 2011-04-28, Steven D'Aprano  wrote:

> While it is common, it is also an abuse of NANs to use it to
> represent missing values. In Python, that's (probably) best done with
> None.

None won't propogate through calculations to produce None's on outputs.

> The statistics language R has a specific value NA to use for missing,
> distinct from NANs.
>
> Still, it could be worse... I've seen a programs use  to
> represent missing values, on the basis that nobody could ever have
> more than (say) 5000 invoices in the database... 

All 1's in a float is a NaN, so all 9's in a BCD value is a NaN.  Sort
of makes sense if the BCD operations propogate "all-nine" values or
raise exceptions when they are encountered (that's a big if).

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Re: [OT] VCS tools

[Ben Finney]

Martin Schöön  writes:

> This has been a pretty informative thread so far. Please keep it coming.
> I am a hardware development guy and do very little software development.
> I have been vaguely aware of tools for version control but inspired by
> this thread I have started looking at Mercurial.

After my passionate Bazaar evangelism? :-)

I seriously recommend anyone looking for a modern VCS to give Bazaar a
decent trial. It's the one I've found newcomers learn most easily, and
it's astoundingly flexible as one's needs with it grow.

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  `\   |
_o__)  |
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Re: Python 3.2 Tkinter and TTK

[Terry Reedy]

On 4/28/2011 1:33 PM, steven.oldner wrote:

Just downloaded Python3.2 from python's site and attempted to run some
of the examples in the 24.2.10 Tk Styling.  The button worked,


I found 4 examples, none of which *do* anything. Perhaps they are only 
meant to show syntax. I am running WinXP. You?


.Style:
.configure OK
.map OK
.layout OK? Text says "it is not intended to do anything useful"
and indeed the displayed button does nothing when pressed.
.theme_settings OK? I do not see any green or olive


but the menu didn't.


What do *you* mean by 'did not work'?

They all compile and display something, but I would have to study more 
before I would know what to expect. It is possible that the examples 
have bugs, or that the ttk module does. Either should be reported on the 
tracker. Others have used it though.


> I also tried a couple from the TKDocs web site.  Only

errors from there.


Syntax error? Runtime exception? or just not look/act as you expect?

--
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Re: Composition instead of inheritance

[Ben Finney]

Ethan Furman  writes:

> For anybody interested in composition instead of multiple inheritance,
> I have posted this recipe on ActiveState (for python 2.6/7, not 3.x):
>
> http://code.activestate.com/recipes/577658-composition-of-classes-instead-of-multiple-inherit/
>
> Comments welcome!

It doesn't look like composition at all, though. I understand
composition to be the setting of attributes on a class or instance; that
recipe doesn't show it very well IMO.

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Re: Read-write lock for Python

[Ben Finney]

Geoff Bache  writes:

> I currently find myself needing a Python read-write lock.

Please tell us what you mean by “read-write lock”.

> I note that there is none in the standard library, but googling
> "python read-write lock" quickly produced 6 different competing
> examples, including two languishing patch proposals for the standard
> library.

That's probably because the term isn't well defined. What is your
definition?

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Re: NaN

[Terry Reedy]

On 4/28/2011 2:59 PM, Steven D'Aprano wrote:


Still, it could be worse... I've seen a programs use  to represent
missing values, on the basis that nobody could ever have more than (say)
5000 invoices in the database...

(I wish I was exaggerating.)


All 9s in a field for missing was once standard for Fortran programs.

--
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Re: IDLE lost from Windows menu !

[Terry Reedy]

On 4/28/2011 12:28 PM, Uncle Ben wrote:

I have lost the convenient feature that to edit a .py file I could
right-click on the file name and reach the menu item "Edit with IDLE".

The workaround is not hard, but it wouild be nice to get this feature
back.

It happened when I was mungeing around and downloaded Python 2.3.3 in
addition to Python 2.71, and got into trojuble uintil I discovered
that I was involuntarily RUNNING the older version.  So I cleaned it
out, but still I have this aftermath.

Is there a Windows guru out there who can tell be how to add to the
right-click menu clicking on myfile.py?


In Window98, one could get from Explorer Window to a file-associations 
dialog/window/tool that would let you change/add 'open', 'open with x', 
'run', for a particular file type without using the registry editor, 
which is slightly dangerous. I have forgotten how to find it in xp, and 
no idea in w7. I would look in windows help and or control panel.


--
Terry Jan Reedy

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Re: Python 3.2 Tkinter and TTK

[David Phillips]

> If you want to programm GUI's it is better for you learn Qt or GTK. They are 
> so much better than tkinter.
> I told this with sadness because I like free things, but the reality is not 
> like this. This libs are in all places.
> 
> ---
> Jayme Proni Filho
> 

My experience with tkinter and Python 3.2 is more positive. I wrote a GUI for 
an editing program (editing like publishers think of it, not programmers) that 
was fairly complex with three different list boxes, an information pane, a 
toolbar, and a pane for the text being edited (implemented with a Text widget). 
 Admittedly it took a little trial and error to perfect the layout of the 
various frames, but when it was done, I was pleased with the appearance, 
functionality, and performance.

David Phillips
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Re: IDLE lost from Windows menu !

[Andrew Berg]

On 2011.04.28 02:11 PM, Uncle Ben wrote:
> It was suggested to me privately that I search for
> HKEY_CLASSES_ROOT\*\shell,
> right_click on "shell",
> create a new key called "EDIT with IDLE"
> and another called "command python.exe %1"
The key you're looking for is HKCR\Python.File\shell. Add a subkey
called Edit with IDLE. Create a subkey in there called command. Inside
HKCR\Python.File\shell\Edit with IDLE\command, modify the default value
to "C:\Python32\pythonw.exe" "C:\Python32\Lib\idlelib\idle.pyw" -e "%1"
(changing the paths if necessary). Do the same with
HKCR\Python.NoConFile\shell to get the command for .pyw files.
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Fwd: subclassing an extension (non built-in) class / type in python 3.2

[Marc Gronle]

Hello everybody,

I read in the extending and embedding documentation of python 3, that it is 
easily possible to subclass or subtype a built-in type. However, in my case, I 
would like to subclass a class, defined in a external python-file (py), which I 
can import in my C++-application and access the class by the module's 
dictionary.

Does anybody have an example or just a hint, how to successfully realize this 
type of inheritance?

I will be grateful for every response.

Cheers

Marc



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subclassing an extension (non built-in) class / type in python 3.2

[Marc Gronle]

Hello everybody,

I read in the extending and embedding documentation of python 3, that it is 
easily possible to subclass or subtype a built-in type. However, in my case, I 
would like to subclass a class, defined in a external python-file (py), which I 
can import in my C++-application and access the class by the module's 
dictionary.

Does anybody have an example or just a hint, how to successfully realize this 
type of inheritance?

I will be grateful for every response.

Cheers

Marc
-- 
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Re: use of index (beginner's question)

[Rhodri James]

On Thu, 28 Apr 2011 01:49:33 +0100, Chris Angelico 
wrote:


On Thu, Apr 28, 2011 at 10:42 AM, Rusty Scalf  wrote:

list1 = ['pig', 'horse', 'moose']
list2 =  ['62327', '49123', '79115']
n = 2
s2 = "list" + `n`
a = s2[list1.index('horse')]
print a


s2 is a string with the value "list2"; this is not the same as the
variable list2. You could use eval to convert it, but you'd do better
to have a list of lists:

lists = [
 ['pig', 'horse', 'moose']
 ['62327', '49123', '79115']
]

Then you could use:
n = 2
a = lists[n][list1.index('horse')]


*cough* I think you mean

n = 1
a = lists[n][list[0].index('horse')]

The alternative would be to have a dictionary of lists:

lists = {
"list1": ['pig', 'horse', 'moose'],
"list2": ['62327', '49123', '79115']
}

n = 2
s2 = "list" + str(n)
a = lists[s2][lists["list1"].index('horse')]

Both of these can be made less ugly if the list you want to index into
isn't one of the lists you might want to look up, but that's just a detail.

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Re: [OT] VCS tools (was "Development tools and practices for Pythonistas")

[Martin Schöön]

This has been a pretty informative thread so far. Please keep it coming.
I am a hardware development guy and do very little software development.
I have been vaguely aware of tools for version control but inspired by
this thread I have started looking at Mercurial.

My humble contribution (from my boss really) since I have not seen it
mentioned here:
http://code.google.com/p/gource/ (I have zero experience of gource so
there is no point in asking me questions)

/Martin
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Re: NaN

[Grant Edwards]

On 2011-04-28, Chris Rebert  wrote:

>> 2. What are the use cases for NaN?  Looks like it gets used a lot as a
>> numeric (float?) object with non-value.
>
> FWICT, it's useful in lower-level languages (which typically lack
> exceptions and often lack nice ways of returning multiple values from
> a function) as a convenient way of signaling a mathematical error.

When doing stuff involving process control systems, I found it very
useful to use NaN to indicate "unknown/invalid".  It propogates
properly through calculations so that when you have an invalid input,
all of the outputs that depend on it also go invalid.

The other option is to use a value/status tuple everywhere you would
normally use a float.  But that falls over every time you need to use
a library function that expects a float as an input and returns a
float as an output.

Since the sensors return a NaN when the value is unkown/invalid it
seemed logical to continue with that paradigm in my Python code -- and
it pretty much "just works".

-- 
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Re: Read-write lock for Python

[Geoff Bache]

On Thu, Apr 28, 2011 at 7:53 PM, D'Arcy J.M. Cain  wrote:
> On Thu, 28 Apr 2011 19:14:45 +0200
> Geoff Bache  wrote:
>> On Thu, Apr 28, 2011 at 4:28 PM, Jean-Michel Pichavant
>>  wrote:
>> > What about
>> >
>> > http://docs.python.org/library/threading.html#lock-objects
>>
>> Those aren't read-write locks. They are basic locks, which don't
>> distinguish between readers and writers. I need to be able to lock
>> between reader and writer operations, without readers locking each
>> other out.
>
> There really isn't any such thing as "read-write" locks.

Did you google it? I even provided the exact search terms to use in my
initial posting. It takes you straight to two standard library patch
proposals and four other solutions, all labelled this way (sometimes
"reader-writer locks" admittedly). That doesn't happen if it isn't a
standard problem.

I'm not looking for general advice on how to solve some specific
problem. I'm asking if anyone knows anything about the relative merits
of the above 6 solutions.

Regards,
Geoff Bache
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Re: IDLE lost from Windows menu !

[Uncle Ben]

On Apr 28, 3:29 pm, MRAB  wrote:
> On 28/04/2011 20:11, Uncle Ben wrote:
>
>
>
> > On Apr 28, 12:28 pm, Uncle Ben  wrote:
> >> I have lost the convenient feature that to edit a .py file I could
> >> right-click on the file name and reach the menu item "Edit with IDLE".
>
> >> The workaround is not hard, but it wouild be nice to get this feature
> >> back.
>
> >> It happened when I was mungeing around and downloaded Python 2.3.3 in
> >> addition to Python 2.7.1, and got into trouble until I discovered
> >> that I was involuntarily RUNNING the older version.  So I cleaned it
> >> out, but still I have this aftermath.
>
> >> Is there a Windows guru out there who can tell be how to add to the
> >> right-click menu clicking on myfile.py?
>
> >> Uncle Ben
>
> > It was suggested to me privately that I search for
> > HKEY_CLASSES_ROOT\*\shell,
> > right_click on "shell",
> > create a new key called "EDIT with IDLE"
> > and another called "command python.exe %1"
>
> > Problem:
> >    Searching on the HKEY group as above yields no "shell".
>
> > Did I not do it right, or is there another way?
>
> > (I would think that that command would execute my file, not edit it.
> > But maybe I will be surprised.)
>
> > (I am running Windows 7, 64-bit.)
>
> Probably the simplest solution would be to install the appropriate
> version of Python again.- Hide quoted text -
>
> - Show quoted text -

Tried that.  No change.  Strange things are happening!
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Re: Deditor

[Kruptein]

On 28 apr, 07:46, jmfauth  wrote:
> On 27 avr, 19:22, Alec Taylor  wrote:
>
> > Thanks, any plans for a Windows version?
>
> - Download the deb
> - Unpack it with a utility like 7zip
> - Throw away the unnecessary stuff, (keep the "deditor part")
> - Depending on your libs, adatpt the "import"
> - Launch deditor.py
> - Then ...
>
> [5 minutes]
>
> In fact, this kind of app can be simply packed in a zip file.
>
> jmf

It isn't that easy as you might have hoped ;)  I'm using wxpython for
rendering the GUI  somehow some things that work in the linux version
break in the windows version  so I need to do some small
modifications  and as I'm a hardcore linux fan I ony use windows for
gaming it usually takes a little longer for a windows release,  I'm
releasing a tarball now btw :D
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Re: Python 3.2 Tkinter and TTK

[Jayme Proni Filho]

Man,

If you want to programm GUI's it is better for you learn Qt or GTK. They are
so much better than tkinter.
I told this with sadness because I like free things, but the reality is not
like this. This libs are in all places.

---
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Skype: jaymeproni
Twitter: @jaymeproni
Phone: +55 - 17 - 3631 - 6576
Mobile: +55 - 17 - 9605 - 3560
e-Mail: jaymeproni at yahoo dot com dot br
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Re: socket.gethostbyaddr() wrongly returning a DNS CNAME as the 'primary' hostname

[cjblaine]

Thanks for the reply, Ned.

Bummer for me.  Check this out:

C code on Solaris 10 SPARC returns the following with nscd
running (the Solaris Naming Services Caching Daemon, on by
default):

  PRIMARY according to gethostbyaddr(): my-dns-cname.our.org
  ALIAS according to gethostbyaddr(): primary.our.org

  However, I can stop/start nscd and get the complete opposite
  (correct) result.

C code on Solaris 10 SPARC returns the following with nscd
OFF:

  PRIMARY according to gethostbyaddr(): my-dns-cname.our.org
  ALIAS according to gethostbyaddr(): primary.our.org

  These then ALTERNATE consistently with every successive
  invocation of my code.

C code on Linux 2.6 with glibc 2.5 returns:

  PRIMARY according to gethostbyaddr(): primary.our.org
  [ no aliases get listed ]

Time to query the corporate DNS folks.
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Re: Have you read the Python docs lately?

[Vinay Sajip]

On Apr 28, 12:40 am, Ben Finney  wrote:

> This one in particular was sorely needed, especially its early if-then
> discussion of whether to use ‘logging’ at all.

For that "when to use logging" part, you can thank Nick Coghlan :-)

Thanks are also due to all those who commented on early drafts, which
were put together initially for the 3.2 release. If anyone has any
other improvements to suggest, keep 'em coming!

Regards,

Vinay Sajip
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Where to start in writing test programs for electronics

[Manatee]

I would like to write test programs that will collect data over the
serial port, control instruments, plot data as its collected, and save
that data to a file. I have partially figured out instrument control
and have downloaded numpy and matplot. I am having trouble pulling it
together as regards feeding realtime data into matplot. I am reading
as much as I can in all areas and I'm hoping someone can give me some
guidance or tips as to how best to proceed with this. Thanks in
advance.
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Zope with mySQL

[harryjatt]

Hi, i am doing web development with Zope. My connected database is mySQL. I
am new to this combination.I have to upload the files to mySQL with
programming in zope and then downloading them via zope.Can you help me in
this regard? I will be very thankfull to you.
Regards, Harry
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Re: socket.gethostbyaddr() wrongly returning a DNS CNAME as the 'primary' hostname

[Ned Deily]

In article 
<850c85c0-be6e-4eec-b6b1-5c79e1716...@glegroupsg2000goo.googlegroups.com
>, cjblaine  wrote:
> Python 2.7.1 (perhaps others)
> 
> I believe this is a bug.  Comments?
> 
> Docs state: Return a triple (hostname, aliaslist, ipaddrlist)
> where hostname is the primary host name responding to the
> given ip_address, aliaslist is a (possibly empty) list of
> alternative host names  for the same address, and ipaddrlist
> is a list of IPv4/v6 addresses for the same interface on the
> same host (most likely containing only a single address).
> 
> my-dns-cname.our.org is a CNAME record for primary.our.org
> primary.our.org has IP address xx.xx.xx.xx
> 
> import socket
> socket.gethostbyaddr('xx.xx.xx.xx')
> 
> returns:
> 
> ('my-dns-cname.our.org', ['primary.our.org'], ['xx.xx.xx.xx'])

socket.gethostbyaddr() is pretty much just a transparent wrapper around 
the platform's C library function of the same name.  See if a simple C 
program with a similar call to gethostbyaddr produces the same results.  
The code in question for Python 2.7 is here:

http://hg.python.org/cpython/file/a6b772599594/Modules/socketmodule.c

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

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Re: IDLE lost from Windows menu !

[MRAB]

On 28/04/2011 20:11, Uncle Ben wrote:

On Apr 28, 12:28 pm, Uncle Ben  wrote:

I have lost the convenient feature that to edit a .py file I could
right-click on the file name and reach the menu item "Edit with IDLE".

The workaround is not hard, but it wouild be nice to get this feature
back.

It happened when I was mungeing around and downloaded Python 2.3.3 in
addition to Python 2.7.1, and got into trouble until I discovered
that I was involuntarily RUNNING the older version.  So I cleaned it
out, but still I have this aftermath.

Is there a Windows guru out there who can tell be how to add to the
right-click menu clicking on myfile.py?

Uncle Ben


It was suggested to me privately that I search for
HKEY_CLASSES_ROOT\*\shell,
right_click on "shell",
create a new key called "EDIT with IDLE"
and another called "command python.exe %1"

Problem:
   Searching on the HKEY group as above yields no "shell".

Did I not do it right, or is there another way?

(I would think that that command would execute my file, not edit it.
But maybe I will be surprised.)

(I am running Windows 7, 64-bit.)


Probably the simplest solution would be to install the appropriate
version of Python again.
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Re: IDLE lost from Windows menu !

[Uncle Ben]

On Apr 28, 12:28 pm, Uncle Ben  wrote:
> I have lost the convenient feature that to edit a .py file I could
> right-click on the file name and reach the menu item "Edit with IDLE".
>
> The workaround is not hard, but it wouild be nice to get this feature
> back.
>
> It happened when I was mungeing around and downloaded Python 2.3.3 in
> addition to Python 2.7.1, and got into trouble until I discovered
> that I was involuntarily RUNNING the older version.  So I cleaned it
> out, but still I have this aftermath.
>
> Is there a Windows guru out there who can tell be how to add to the
> right-click menu clicking on myfile.py?
>
> Uncle Ben

It was suggested to me privately that I search for
HKEY_CLASSES_ROOT\*\shell,
right_click on "shell",
create a new key called "EDIT with IDLE"
and another called "command python.exe %1"

Problem:
  Searching on the HKEY group as above yields no "shell".

Did I not do it right, or is there another way?

(I would think that that command would execute my file, not edit it.
But maybe I will be surprised.)

(I am running Windows 7, 64-bit.)

Uncle Ben
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Re: NaN

[Steven D'Aprano]

On Thu, 28 Apr 2011 10:01:49 -0700, Chris Rebert wrote:

> > 2. What are the use cases for NaN?  Looks like it gets used a lot as a
> > numeric (float?) object with non-value.
> 
[...]
> And it's
> used to represent missing numeric data values, sort of like a
> numerical None/Null: "How much does the truck weigh? NaN (i.e. No
> idea; we haven't put it on the scale yet)."

While it is common, it is also an abuse of NANs to use it to represent 
missing values. In Python, that's (probably) best done with None. The 
statistics language R has a specific value NA to use for missing, 
distinct from NANs.

Still, it could be worse... I've seen a programs use  to represent 
missing values, on the basis that nobody could ever have more than (say) 
5000 invoices in the database... 

(I wish I was exaggerating.)


-- 
Steven
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Re: Composition instead of inheritance

[Jean-Michel Pichavant]

Ethan Furman wrote:
For anybody interested in composition instead of multiple inheritance, 
I have posted this recipe on ActiveState (for python 2.6/7, not 3.x):


http://code.activestate.com/recipes/577658-composition-of-classes-instead-of-multiple-inherit/ 



Comments welcome!

~Ethan~

Sounds great. But I fear that would completely fool any linter.

JM
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Re: I think I found a mistake in the official language reference documentation -- or I am missing somethig???

[Igor Soares]

On 27 abr, 21:29, MRAB  wrote:
> On 27/04/2011 21:02, Igor Soares wrote:
>
>
>
>
>
>
>
>
>
> > Reading the section "6.11. The import statement"
> >http://docs.python.org/py3k/reference/simple_stmts.html#the-import-st...
>
> > I found:
> > """
> > Import statements are executed in two steps: (1) find a module, and
> > initialize it if necessary; (2) define a name or names in the local
> > namespace (of the scope where the import statement occurs).
> > (...)
> > The first form (without from) repeats these steps for each identifier
> > in the list. The form with from performs step (1) once, and then
> > performs step (2) repeatedly.
> > """
> > In the last sentence, isn't it the opposite?
> > With the "from" form it would find/initialize all the modules and
> > define just the name after "from".
> > Or am I missing something?
>
> The "from" form is like:
>
>      from monty import spam, eggs
>
> The steps are:
>
> 1. find module "monty", and initialize it if necessary
>
> 2. define name "spam" in the local namespace
>
> 3. define name "eggs" in the local namespace
>
> Also note that the name "monty" itself never enters the local namespace.

My mistake...
I got confused with wrong code in IDLE...
I also didn't understand that section ( 6.11 ) at first

Thank you guys for the help
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Re: Read-write lock for Python

[D'Arcy J.M. Cain]

On Thu, 28 Apr 2011 19:14:45 +0200
Geoff Bache  wrote:
> On Thu, Apr 28, 2011 at 4:28 PM, Jean-Michel Pichavant
>  wrote:
> > What about
> >
> > http://docs.python.org/library/threading.html#lock-objects
> 
> Those aren't read-write locks. They are basic locks, which don't
> distinguish between readers and writers. I need to be able to lock
> between reader and writer operations, without readers locking each
> other out.

There really isn't any such thing as "read-write" locks.  In fact, the
term "locks" without any further explanation is pretty loose in any
case.  You can use the above method to implement your own locking
scheme.  However, that only works if your application is a single,
multi-threaded app.  Is that the case?  When I saw your original
question I thought that you needed something inter-process.  If so then
you need another scheme.

I think you have to first clarify your requirements and ask again.  I
have gleaned a little more information from your above response, you
don't require readers to be locked out during an update if I understand
the requirement.  There is still a lot of information missing.  For
example:

 - What is being read and written?  Files?
 - Is this a single multi-threaded app or multiple processes?
 - if multiple processes, can they be counted on to cooperate?
 - Do update requests need to be queued or is random availability OK?

Now, don't just answer the above questions. Try to start with that and
think about what other requirements you have.  The more information you
give us, the better the answer will be.  You may even find that locking
is not the actual answer you need.  People do have a tendency to offer
solutions when they think they are asking questions.  Don't pre-suppose
the answer.

http://www.catb.org/~esr/faqs/smart-questions.html is always a good
read in these situations.

-- 
D'Arcy J.M. Cain  |  Democracy is three wolves
http://www.druid.net/darcy/|  and a sheep voting on
+1 416 425 1212 (DoD#0082)(eNTP)   |  what's for dinner.
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Re: Composition instead of inheritance

[Eric Snow]

On Thu, Apr 28, 2011 at 11:15 AM, Ethan Furman  wrote:

> For anybody interested in composition instead of multiple inheritance, I
> have posted this recipe on ActiveState (for python 2.6/7, not 3.x):
>
>
> http://code.activestate.com/recipes/577658-composition-of-classes-instead-of-multiple-inherit/
>
> Comments welcome!
>
> ~Ethan~
> --
> http://mail.python.org/mailman/listinfo/python-list
>

That's cool.  And if Spam and Eggs were abstract base classes you could
register TestAll to them.  Granted, that is not so applicable in your
example.   But generally that would help bridge the inheritance gap for
isinstance cases.

-eric

p.s. I would have commented on the recipe but could not log in...
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Python 3.2 Tkinter and TTK

[steven.oldner]

Just downloaded Python3.2 from python's site and attempted to run some
of the examples in the 24.2.10Tk Styling.  The button worked, but the
menu didn't.  I also tried a couple from the TKDocs web site.  Only
errors from there.

So, what do I need to do to get it to run?
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Re: NaN

[Eric Snow]

On Thu, Apr 28, 2011 at 11:01 AM, Chris Rebert  wrote:

> On Thu, Apr 28, 2011 at 9:21 AM, Eric Snow 
> wrote:
> > There's a big discussion going on at python-dev and python-ideas about
> NaN
> > (not-a-number, from IEEE 754).  I haven't really gotten into any
> scientific
> > computing or numeric programming so I have never knowingly dealt with
> NaN.
> >  However, I have read the discussions and several things are not clear:
> > 1. Why is NaN not an exception?  (not "why not change it to one?"
>  Changing
> > it now would probably break stuff.)
>
> Most things that would produce NaN [e.g. x/0, sqrt(-abs(x))] in
> lower-level languages do produce exceptions in Python. If you
> encounter a NaN in Python, it was probably either explicitly created
> or came from a C extension library. It's basically an abstraction
> leaked through from C/hardware for compatibility.
>
> > 2. What are the use cases for NaN?  Looks like it gets used a lot as a
> > numeric (float?) object with non-value.
>
> FWICT, it's useful in lower-level languages (which typically lack
> exceptions and often lack nice ways of returning multiple values from
> a function) as a convenient way of signaling a mathematical error. It
> also lets some calculations continue to limp along (albeit with a NaN
> result) after an error rather than forcing the probably slower
> explicit handling of the error at the time of its occurrence. And it's
> used to represent missing numeric data values, sort of like a
> numerical None/Null: "How much does the truck weigh? NaN (i.e. No
> idea; we haven't put it on the scale yet)."
>

Thanks Chris.  That's really helpful.  Sounds like NaN is a pretty
overloaded object.  Nick Coghlan brought up in the issue tracker that it is
useful for prototyping algorithms that will be converted to C.  Other than
that, why should Python care?  We have None.  Is it for performance (since
None acts like a number in some ways, but NaN acts like it better)?

Is the problem less with NaN (number object with an undefined value) and
more with the broken reflexivity with regards to equality in general ("x is
x" doesn't imply that "x == x")?  Looks like that situation breaks a number
of different operations in Python, whether or not NaN is involved.

This stuff is way outside my realm of experience so I don't want to wade
into the core lists with these questions, but I want to understand the
issues too...

-eric


> Cheers,
> Chris
> --
> http://rebertia.com
>
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Re: Equivalent code to the bool() built-in function

[Duncan Booth]

Albert van der Horst  wrote:

>>I guess I never thought about it, but there isn't an 'xor' operator to
>>go along with 'or' and 'and'.  Must not be something I need very often.
> 
> There is. <> applied to booleans is xor.
> 
Best to get into the habit of using '!=' otherwise you'll find Python 3.x a 
bit frustrating.

However, that only works if you have exactly two values: both 'and' and 
'or' will extend easily to any number of values:

 >>> True and False and True
 False
 >>> False or False or True or False
 True

but using != for 'xor' doesn't extend the same way:

 >>> False != False != True
 False

You can use 'sum(...)==1' for a larger number of values but do have to be 
careful that all of them are bools (or 0|1).

-- 
Duncan Booth http://kupuguy.blogspot.com
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Re: Read-write lock for Python

[Geoff Bache]

On Thu, Apr 28, 2011 at 4:28 PM, Jean-Michel Pichavant
 wrote:
> Geoff Bache wrote:
>>
>> Hi all,
>>
>> I currently find myself needing a Python read-write lock. I note that
>> there is none in the standard library, but googling "python read-write
>> lock" quickly produced 6 different competing examples, including two
>> languishing patch proposals for the standard library.
>>
>> I can always pick a random one and hope for the best, but I was hoping
>> someone here might have a tip for one that has been used and debugged
>> and is likely to work.
>>
>> Regards,
>> Geoff Bache
>>
>
> What about
>
> http://docs.python.org/library/threading.html#lock-objects

Those aren't read-write locks. They are basic locks, which don't
distinguish between readers and writers. I need to be able to lock
between reader and writer operations, without readers locking each
other out.

/Geoff
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Re: use of index (beginner's question) (Iain King)

[Apprentice3D]

Envoyé de mon iPad

Le 2011-04-28 à 4:55, python-list-requ...@python.org a écrit :

> Send Python-list mailing list submissions to
>python-list@python.org
> 
> To subscribe or unsubscribe via the World Wide Web, visit
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> or, via email, send a message with subject or body 'help' to
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> 
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of Python-list digest..."
> Today's Topics:
> 
>   1. Re: Have you read the Python docs lately? (Terry Reedy)
>   2. Re: Reliably call code after object no longer exists or is
>  "unreachable"? (Gregory Ewing)
>   3. argparse parser stores lists instead of strings (Andrew Berg)
>   4. Re: unpickling derived LogRecord in python 2.7 from python2.6
>  (Peter Otten)
>   5. Re: Access violation reading 0x0010 (yuan zheng)
>   6. Re: argparse parser stores lists instead of strings (Peter Otten)
>   7. Re: use of index (beginner's question) (Iain King)
>   8. Re: argparse parser stores lists instead of strings
>  (Gabriel Genellina)
>   9. Re: Access violation reading 0x0010 (Gabriel Genellina)
>  10. Spurious character in IOError exception (loial)
> 
> 
> 
> 
> Ce message ne peut être affiché à cause de son format. Veuillez demander à 
> l’expéditeur de le renvoyer en utilisant un autre format ou un autre logiciel 
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> 
> 
> 
> 
> 
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Re: Python IDE/text-editor

[Alec Taylor]

Your probably right.

I suppose I'll just wait till I finish my fooIDE project

> On Fri, Apr 29, 2011 at 2:21 AM, Albert van der Horst
>  wrote:
>> In article ,
>> Alec Taylor   wrote:
>>>Geany I've tried in the past, it's really buggy on my home computer
>>>and at Uni... however from my phone it works wonderfully! (Use it for
>>>C++ projects on Rhobuntu)
>>>
>>>Eric 4 was suggested to me on the #python channel on Freenode...
>>>however I've never been able to get it compiled/working. Too many
>>>dependencies I'm guessing...
>>>
>>>PTK looks great, and does everything I want (from screenshots).
>>>Unfortunately, it doesn't run on my system; Win7 x64, Python 2.7.1
>>>x64, WxPython 2.8 x64. Install ran as admin.
>>>
>>>Emacs and vim still seem like good alternatives, when I get the time.
>>>However, currently have 3 assignments to start and finish so would
>>>like a simple Notepad2 with python interpreter attached (and keyboard
>>>shortcut to run script) type program.
>>>
>>>Please continue recommending
>>>
>>>Thanks,
>>>
>>>Alec Taylor
>>
>> You will never be satisfied, until you've written something yourself.
>> Start writing now. A friend of mine started writing in 1983,
>> and since 1985 I'm a happy user. The only language that is a candidate
>> to write in is C, however.
>>
>> Groetjes Albert
>>
>> --
>> --
>> Albert van der Horst, UTRECHT,THE NETHERLANDS
>> Economic growth -- being exponential -- ultimately falters.
>> albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst
>>
>> --
>> http://mail.python.org/mailman/listinfo/python-list
>>
>
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Composition instead of inheritance

[Ethan Furman]

For anybody interested in composition instead of multiple inheritance, I 
have posted this recipe on ActiveState (for python 2.6/7, not 3.x):


http://code.activestate.com/recipes/577658-composition-of-classes-instead-of-multiple-inherit/

Comments welcome!

~Ethan~
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Re: NaN

[Chris Rebert]

On Thu, Apr 28, 2011 at 9:21 AM, Eric Snow  wrote:
> There's a big discussion going on at python-dev and python-ideas about NaN
> (not-a-number, from IEEE 754).  I haven't really gotten into any scientific
> computing or numeric programming so I have never knowingly dealt with NaN.
>  However, I have read the discussions and several things are not clear:
> 1. Why is NaN not an exception?  (not "why not change it to one?"  Changing
> it now would probably break stuff.)

Most things that would produce NaN [e.g. x/0, sqrt(-abs(x))] in
lower-level languages do produce exceptions in Python. If you
encounter a NaN in Python, it was probably either explicitly created
or came from a C extension library. It's basically an abstraction
leaked through from C/hardware for compatibility.

> 2. What are the use cases for NaN?  Looks like it gets used a lot as a
> numeric (float?) object with non-value.

FWICT, it's useful in lower-level languages (which typically lack
exceptions and often lack nice ways of returning multiple values from
a function) as a convenient way of signaling a mathematical error. It
also lets some calculations continue to limp along (albeit with a NaN
result) after an error rather than forcing the probably slower
explicit handling of the error at the time of its occurrence. And it's
used to represent missing numeric data values, sort of like a
numerical None/Null: "How much does the truck weigh? NaN (i.e. No
idea; we haven't put it on the scale yet)."

Cheers,
Chris
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Re: Equivalent code to the bool() built-in function

[buck]

I'm not not touching you!
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Re: Have you read the Python docs lately?

[Raymond Hettinger]

On Apr 27, 11:28 pm, Paul Rubin  wrote:
> Raymond Hettinger  writes:
> > A number of developers have been working on adding examples and useful
> > advice to the docs.  To sharpen your skills, here are some pieces of
> > recommended reading:
>
> Thanks, those are nice.  The logging one looks especially useful.  The
> module always looked very confusing to me (too Java-like), and I've
> dreaded the day when I might have to figure out how to use it instead of
> my own ad-hoc logging.  I can sleep better now ;-).

Vinay put also put together a logging cookbook:

   http://docs.python.org/howto/logging-cookbook.html


Raymond
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multiprocessing: file-like object

[buck]

I've been having issues with getting a file-like object to work with 
multiprocessing. Since the details are quite lengthy, I've posted them on 
stackoverflow here: 
http://stackoverflow.com/questions/5821880/python-multiprocessing-synchronizing-file-like-object

I hope I'm not being super rude by cross-posting, but I thought some of you 
would be interested in the question, and I'd be delighted to get some ideas.
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IDLE lost from Windows menu !

[Uncle Ben]

I have lost the convenient feature that to edit a .py file I could
right-click on the file name and reach the menu item "Edit with IDLE".

The workaround is not hard, but it wouild be nice to get this feature
back.

It happened when I was mungeing around and downloaded Python 2.3.3 in
addition to Python 2.71, and got into trojuble uintil I discovered
that I was involuntarily RUNNING the older version.  So I cleaned it
out, but still I have this aftermath.

Is there a Windows guru out there who can tell be how to add to the
right-click menu clicking on myfile.py?

Uncle Ben
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NaN

[Eric Snow]

There's a big discussion going on at python-dev and python-ideas about NaN
(not-a-number, from IEEE 754).  I haven't really gotten into any scientific
computing or numeric programming so I have never knowingly dealt with NaN.
 However, I have read the discussions and several things are not clear:

1. Why is NaN not an exception?  (not "why not change it to one?"  Changing
it now would probably break stuff.)
2. What are the use cases for NaN?  Looks like it gets used a lot as a
numeric (float?) object with non-value.

Any clarification would be really helpful.  Thanks!

-eric
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socket.gethostbyaddr() wrongly returning a DNS CNAME as the 'primary' hostname

[cjblaine]

Python 2.7.1 (perhaps others)

I believe this is a bug.  Comments?

Docs state: Return a triple (hostname, aliaslist, ipaddrlist)
where hostname is the primary host name responding to the
given ip_address, aliaslist is a (possibly empty) list of
alternative host names  for the same address, and ipaddrlist
is a list of IPv4/v6 addresses for the same interface on the
same host (most likely containing only a single address).

my-dns-cname.our.org is a CNAME record for primary.our.org
primary.our.org has IP address xx.xx.xx.xx

import socket
socket.gethostbyaddr('xx.xx.xx.xx')

returns:

('my-dns-cname.our.org', ['primary.our.org'], ['xx.xx.xx.xx'])
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Re: Equivalent code to the bool() built-in function

[Albert van der Horst]

In article <9142usf51...@mid.individual.net>,
Gregory Ewing   wrote:
>Chris Angelico wrote:
>
>> Remind me some day to finish work on my "ultimate programming
>> language", which starts out with a clean slate and lets the programmer
>> define his own operators and everything.
>
>Didn't someone already do that and call it "lisp"? :-)

Lisp is betrayed by its brackets. He wants Forth.

>
>--
>Greg

Groetjes Albert

--
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Economic growth -- being exponential -- ultimately falters.
albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst

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Re: Equivalent code to the bool() built-in function

[Albert van der Horst]

In article ,
Grant Edwards   wrote:
>
>On Tue, Apr 19, 2011 at 7:09 AM, Christian Heimes  wrote:
>> Am 18.04.2011 21:58, schrieb John Nagle:
>>> ?? ?? This is typical for languages which backed into a "bool" type,
>>> rather than having one designed in. ??The usual result is a boolean
>>> type with numerical semantics, like
>>>
>>> ??>>> True + True
>>> 2
>>
>> I find the behavior rather useful. It allows multi-xor tests like:
>>
>> if a + b + c + d != 1:
>> ?? ??raise ValueError("Exactly one of a, b, c or d must be true.")
>
>I guess I never thought about it, but there isn't an 'xor' operator to
>go along with 'or' and 'and'.  Must not be something I need very often.

There is. <> applied to booleans is xor.

>
>--
>Grant Edwards   grant.b.edwardsYow! I am having FUN...
>  at   I wonder if it's NET FUN or
>  gmail.comGROSS FUN?


--
-- 
Albert van der Horst, UTRECHT,THE NETHERLANDS
Economic growth -- being exponential -- ultimately falters.
albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst

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Re: Python IDE/text-editor

[Albert van der Horst]

In article ,
Alec Taylor   wrote:
>Geany I've tried in the past, it's really buggy on my home computer
>and at Uni... however from my phone it works wonderfully! (Use it for
>C++ projects on Rhobuntu)
>
>Eric 4 was suggested to me on the #python channel on Freenode...
>however I've never been able to get it compiled/working. Too many
>dependencies I'm guessing...
>
>PTK looks great, and does everything I want (from screenshots).
>Unfortunately, it doesn't run on my system; Win7 x64, Python 2.7.1
>x64, WxPython 2.8 x64. Install ran as admin.
>
>Emacs and vim still seem like good alternatives, when I get the time.
>However, currently have 3 assignments to start and finish so would
>like a simple Notepad2 with python interpreter attached (and keyboard
>shortcut to run script) type program.
>
>Please continue recommending
>
>Thanks,
>
>Alec Taylor

You will never be satisfied, until you've written something yourself.
Start writing now. A friend of mine started writing in 1983,
and since 1985 I'm a happy user. The only language that is a candidate
to write in is C, however.

Groetjes Albert

--
-- 
Albert van der Horst, UTRECHT,THE NETHERLANDS
Economic growth -- being exponential -- ultimately falters.
albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst

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Re: Read-write lock for Python

[Jean-Michel Pichavant]

Geoff Bache wrote:

Hi all,

I currently find myself needing a Python read-write lock. I note that
there is none in the standard library, but googling "python read-write
lock" quickly produced 6 different competing examples, including two
languishing patch proposals for the standard library.

I can always pick a random one and hope for the best, but I was hoping
someone here might have a tip for one that has been used and debugged
and is likely to work.

Regards,
Geoff Bache
  

What about

http://docs.python.org/library/threading.html#lock-objects

?

JM
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Read-write lock for Python

[Geoff Bache]

Hi all,

I currently find myself needing a Python read-write lock. I note that
there is none in the standard library, but googling "python read-write
lock" quickly produced 6 different competing examples, including two
languishing patch proposals for the standard library.

I can always pick a random one and hope for the best, but I was hoping
someone here might have a tip for one that has been used and debugged
and is likely to work.

Regards,
Geoff Bache
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Re: Need your help

[Thomas Rachel]

Am 28.04.2011 13:14, schrieb Chris Rebert:


import a, b, sys
def c():
 orig_stdout = sys.stdout
 sys.stdout = open('my_log_file.log', 'w')
 a.a()
 b.b()
 sys.stdout.close()
 sys.stdout = orig_stdout


Someone may have written a with-statement context manager that
abstracts away the swapping.


@contextlib.contextmanager
def swap_stdout(target):
orig_stdout = sys.stdout
sys.stdout = target
try:
yield target
finally:
sys.stdout = orig_stdout

In this case, I can use all kinds of files (open() files, StringIO 
objects etc.), and can re-use them if necessary, in order to 
prepend/append data.


Closing can happen additionally, if the user wants.


Thomas
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Re: 回复: Re: Need your help

[Jean-Michel Pichavant]

1011_wxy wrote:

Hi JM:
 
*python c.py > afile.log* 
 
 
could you pls give me the whole example?

I am so sorry that I am a beginner in Python.


Your module a and  b that you cannot modify given your original 
description, are printing data using the print statement.
That means these module only intend to print the data on the standard 
output (aka stdout, your screen by default).


If you want to print the data in a file, then you have to make stdout 
that file. 2 possible way have been provided:


1/ within the c.py file, redirect sys.stdout to a file (see Chris 
Rebert's answer)
2/ use the system command line to redirect stdout to a file. In any unix 
system, you can redirect stdout to a file( instead of the screen) that way:


   echo "Hello world" > afile.txt

It works for any command, including

   python c.py > afile.txt


That will execute you c.py file writing everything into afile.txt 
instead of your display.


JM
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回复: Re: Need your help

[1011_wxy]

Hi JM:

python c.py > afile.log 


could you pls give me the whole example?
I am so sorry that I am a beginner in Python.


2011-04-28



1011_wxy



发件人: Jean-Michel Pichavant 
发送时间: 2011-04-28 20:42
主 题: Re: Need your help
收件人: 1011_wxy <1011_...@163.com>
抄 送: "python-list@python.org" 





1011_wxy wrote: 
> Hi friends: 
>   
> Here I need some help. 
>   
> #encoding="utf-8" 
> #moudle a.py 
> def a(): 
> print " function a!" 
>   
> #encoding="utf-8" 
> #moudle b.py 
> def b(): 
> print " function b!" 
>   
>   
> #encoding="utf-8" 
> #moudle c.py 
> import a 
> import b 
> def c(): 
> a.a() 
> b.b() 
>   
>   
> Here in function c,How can i record all the information printed by a  
> and b with out modifying moudle a and b? 
> I want to output all the printed information into a text file. 
>   
> Need your help, thanks a lot! 
>   
> Best Regards 
>   
> 2011-04-28 
>  
> Kerry Wang 
Hi, 

python c.py > afile.log 


JM -- 
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High respected career - Careers in next month

[gaurav]

Potential income in Management careers.
Work in Management careers.
Visit: http://managementjobs.webs.com/index.htm 
http://jobscore.webs.com/executivemanager.htm

Careers for Management - Careers in next month
http://employmentsmanagement.blogspot.com/ http://rojgars1.webs.com/gov.htm
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Re: Need your help

[Jean-Michel Pichavant]

1011_wxy wrote:

Hi friends:
 
Here I need some help.
 
#encoding="utf-8"

#moudle a.py
def a():
print " function a!"
 
#encoding="utf-8"

#moudle b.py
def b():
print " function b!"
 
 
#encoding="utf-8"

#moudle c.py
import a
import b
def c():
a.a()
b.b()
 
 
Here in function c,How can i record all the information printed by a 
and b with out modifying moudle a and b?

I want to output all the printed information into a text file.
 
Need your help, thanks a lot!
 
Best Regards
 
2011-04-28


Kerry Wang

Hi,

python c.py > afile.log


JM
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Re: Need your help

[Ervin Hegedüs]

hello,

On Thu, Apr 28, 2011 at 01:20:16PM +0200, Ervin Hegedüs wrote:
> #!/usr/bin/python
> 
> import a
> import b
> 
> import sys
> import StringIO
> 
> output = StringIO.StringIO()
> 
> def c():
> # save default stdout
> tout = sys.stdout
> # redirect stdout to StringIO object
> sys.stdout = output
> # a.a() prints their output to StringIO object
> a.a()
> # back up default stdout
> sys.stdout = tout
> # print StringIO object value
> print "retval:", output.getvalue()
> 
> c()

sorry,

this is a littlebit more abstact example, it gives a StringIO
object, instead of write to a file - of course, you can do what
you want with that string...


a.
 
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Re: Need your help

[Ervin Hegedüs]

hello,

> Here I need some help.
> 
> #encoding="utf-8"
> #moudle a.py
> def a():
> print " function a!"
> 
> #encoding="utf-8"
> #moudle b.py
> def b():
> print " function b!"
> 
> 
> #encoding="utf-8"
> #moudle c.py
> import a
> import b
> def c():
> a.a()
> b.b()
> 
> 
> Here in function c,How can i record all the information printed by a and b 
> with out modifying moudle a and b?
> I want to output all the printed information into a text file.
> 
> Need your help, thanks a lot!

sounds you want something like this:

#!/usr/bin/python

import a
import b

import sys
import StringIO

output = StringIO.StringIO()

def c():
# save default stdout
tout = sys.stdout
# redirect stdout to StringIO object
sys.stdout = output
# a.a() prints their output to StringIO object
a.a()
# back up default stdout
sys.stdout = tout
# print StringIO object value
print "retval:", output.getvalue()

c()



a.
 
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Re: Need your help

[Chris Rebert]

On Wed, Apr 27, 2011 at 10:38 PM, 1011_wxy <1011_...@163.com> wrote:
> Hi friends:
>
> Here I need some help.
>
> #encoding="utf-8"
> #moudle a.py
> def a():
>     print " function a!"
>
> #encoding="utf-8"
> #moudle b.py
> def b():
>     print " function b!"
>
>
> #encoding="utf-8"
> #moudle c.py
> import a
> import b
> def c():
> a.a()
> b.b()
>
>
> Here in function c,How can i record all the information printed by a and b
> with out modifying moudle a and b?
> I want to output all the printed information into a text file.
>
> Need your help, thanks a lot!

import a, b, sys
def c():
orig_stdout = sys.stdout
sys.stdout = open('my_log_file.log', 'w')
a.a()
b.b()
sys.stdout.close()
sys.stdout = orig_stdout


Someone may have written a with-statement context manager that
abstracts away the swapping.

Cheers,
Chris
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Need your help

[1011_wxy]

Hi friends:

Here I need some help.

#encoding="utf-8"
#moudle a.py
def a():
print " function a!"

#encoding="utf-8"
#moudle b.py
def b():
print " function b!"


#encoding="utf-8"
#moudle c.py
import a
import b
def c():
a.a()
b.b()


Here in function c,How can i record all the information printed by a and b with 
out modifying moudle a and b?
I want to output all the printed information into a text file.

Need your help, thanks a lot!

Best Regards

2011-04-28



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Re: use of index (beginner's question)

[Graeme Glass]

On Apr 28, 5:32 am, Algis Kabaila  wrote:
> On Thursday 28 April 2011 11:23:51 Thomas 'PointedEars' Lahn
> wrote:> Chris Angelico wrote:
> > > Rusty Scalf wrote:
> > >> list1 = ['pig', 'horse', 'moose']
> > >> list2 =  ['62327', '49123', '79115']
> > >> n = 2
> > >> s2 = "list" + `n`
> >>> "list" + 'n'
> 'listn'
>
> And IMHO you did not want that, did you?
>
> OldAl.
> --
> Algishttp://akabaila.pcug.org.au/StructuralAnalysis.pdf

It will not be 'listn' it will be 'list2'. He is using back ticks `
which translates the n into its value 2.
Granted it is not very readable (as it can easily be mistaken for a
single quote depending on the font your using). It would be better
written as 'list%s' %n
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Re: Spurious character in IOError exception

[Peter Otten]

loial wrote:

> When I correctly trap an IOError a spurious u' appears in the file
> path in the exception message :
> 
> The path used in the code is correct i.e. /home/myfile
> 
> But the error message says :
> 
> [Errno 2] No such file or directory: u'/home/myfile'
> 
> 
> I am simply doing
> 
>  except IOError, e:
> print str(e)
> 
> 
> Any ideas where the 'u  is coming from?
> 
> This is python 2.4.1

The filename does not appear directly in the error message, it is first 
converted by repr(). This ensures that

(1) the error message will consist only of ascii characters
(2) the filename can reliably reconstructed from the message

>>> try: open("äöü")
... except IOError, e: print e
...
[Errno 2] No such file or directory: '\xc3\xa4\xc3\xb6\xc3\xbc'

but the output may puzzle end users. The u'...' in your case means that you 
passed a unicode string to the open(...) function.

>>> try: open(u"äöü")
... except IOError, e: print e
...
[Errno 2] No such file or directory: u'\xe4\xf6\xfc'

If you are sure that the output device supports unicode output (i. e. has a 
known encoding and can display the characters in your filename) you can 
build a friendlier message

>>> try: open(u"äöü")
... except IOError, e: print u"[Errno %d] %s: %s" % (e.errno, e.strerror, 
e.filename)
...
[Errno 2] No such file or directory: äöü

Be aware though that some problems become near-impossible to detect that 
way:

>>> try: open(u"äöü\n") # note the trailing newline
... except IOError, e: print u"[Errno %d] %s: %s" % (e.errno, e.strerror, 
e.filename)
...
[Errno 2] No such file or directory: äöü

>>>


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Re: How to upload a file

[Gabriel Genellina]

En Wed, 27 Apr 2011 11:14:54 -0300, Torsten Bronger  
 escribió:



Hallöchen!

I'm skimming through the various recipies for uploading a file via
HTTP.  Unfortunately, all of them are awkward but also rather old.
(See for example
http://stackoverflow.com/questions/68477/send-file-using-post-from-a-python-script)

In my module, I do my HTTP request like this:

opener =  
urllib2.build_opener(urllib2.HTTPCookieProcessor(cookielib.CookieJar()))

opener.open(url, urllib.urlencode(data, doseq=True))

Well, and now I'd also like to include a file upload to the POST
data.  The solution should use urllib2, otherwise I'd have to change
most of my existing code.

If you now say "Torsten, unfortunately it *is* so complicated" I'll
jump through the hoops, but I'd love to hear that with Python 2.6.5
there's an easier way.  ;-)


This particular battery isn't included (yet - see  
http://bugs.python.org/issue3244)

but this little library may help:
https://bitbucket.org/chrisatlee/poster

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Gabriel Genellina

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Spurious character in IOError exception

[loial]

When I correctly trap an IOError a spurious u' appears in the file
path in the exception message :

The path used in the code is correct i.e. /home/myfile

But the error message says :

[Errno 2] No such file or directory: u'/home/myfile'


I am simply doing

 except IOError, e:
print str(e)


Any ideas where the 'u  is coming from?

This is python 2.4.1



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Re: Access violation reading 0x00000010

[Gabriel Genellina]

En Thu, 28 Apr 2011 03:35:48 -0300, yuan zheng   
escribió:



Sorry , the path is just an example.

This is not the question I think. Because there is lots of api
in libcommon-0.dll, and there is no fault when invoking other
api, such as libcommon.SIM_start().. It's just fault when invoking
this api -> SIM_init(). So I wanna which situation would lead to this  
error:

--
WindowsError: exception: access violation reading 0x0010
--


On Thu, Apr 28, 2011 at 4:01 PM, yuan zheng 
wrote:
>
> libcommon = CDLL("c:\libcommon-0.dll", RTLD_GLOBAL)
>
> libcommon.SIM_init() -> This is the invoking.


It's hard to guess, but if you get an access violation just from those two  
lines of code, I'd say the problem is inside SIM_init() itself.


It may be attempting to dereference a NULL pointer: accessing a field  
inside a struct, or calling a virtual function from a NULL object...


Also, make sure CDLL is the right choice; it implies a prototype like this:

int cdecl SIM_INIT(void);

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Re: argparse parser stores lists instead of strings

[Gabriel Genellina]

En Thu, 28 Apr 2011 04:24:46 -0300, Andrew Berg  
 escribió:



I've set up groups of arguments for a script I'm writing, and any time I
give an argument a value, it gets stored as a list instead of a string,
even if I explicitly tell it to store a string. Arguments declared with
other types (e.g. float, int) and default values are stored as expected.
For example:

vidin_args=parser.add_argument_group('Video Input Options', 'Various
options that control how the video file is demuxed/decoded.')
vidin_args.add_argument('-m', dest='vmode', nargs=1, type=str,
metavar='video_mode', choices=['ntsc', 'pal', 'film', 'ivtc'],
default='ntsc', help='Valid values are "ntsc", "pal", "film" and  
"ivtc".')

...more arguments...
opts=parser.parse_args()

If I assign a value on the command line (e.g. -m pal), opts.vmode is a
list, otherwise it's a string. This is pretty bad since I can't know
whether to get opts.vmode or opts.vmode[0] later in the script. I could
loop through all the options and convert each option to a string, but
that's not really something I want to do, especially if I start adding
more options.


That's because of nargs=1. From the argparse documentation: [1]

	Note that nargs=1 produces a list of one item. This is different from the  
default, in which the item is produced by itself.


So, just remove nargs=1 from add_argument()

[1] http://docs.python.org/py3k/library/argparse.html#nargs

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Re: use of index (beginner's question)

[Iain King]

On Apr 28, 2:45 am, Chris Angelico  wrote:
> Incidentally, you're allowed to put the comma on the last item too:
>
>  lists = [
>   ['pig', 'horse', 'moose'],
>   ['62327', '49123', '79115'],
> ]
>
> Often makes for easier maintenance, especially when you append
> array/list elements.
>
> Chris Angelico

I did not know this.  Very useful!

Iain
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Re: argparse parser stores lists instead of strings

[Peter Otten]

Andrew Berg wrote:

> I've set up groups of arguments for a script I'm writing, and any time I
> give an argument a value, it gets stored as a list instead of a string,
> even if I explicitly tell it to store a string. Arguments declared with
> other types (e.g. float, int) and default values are stored as expected.
> For example:
> 
> vidin_args=parser.add_argument_group('Video Input Options', 'Various
> options that control how the video file is demuxed/decoded.')
> vidin_args.add_argument('-m', dest='vmode', nargs=1, type=str,
> metavar='video_mode', choices=['ntsc', 'pal', 'film', 'ivtc'],
> default='ntsc', help='Valid values are "ntsc", "pal", "film" and "ivtc".')
> ...more arguments...
> opts=parser.parse_args()
> 
> If I assign a value on the command line (e.g. -m pal), opts.vmode is a
> list, otherwise it's a string. This is pretty bad since I can't know
> whether to get opts.vmode or opts.vmode[0] later in the script. I could
> loop through all the options and convert each option to a string, but
> that's not really something I want to do, especially if I start adding
> more options.
> 
> I'm pretty new to Python, and I might have missed something, but I have
> been looking!

http://docs.python.org/py3k/library/argparse.html#nargs

"""
Note that nargs=1 produces a list of one item. This is different from the 
default, in which the item is produced by itself.
"""

So just omit 'nargs=1' from the add_argument() call.

> In case it matters, I'm learning Python 3.2 and have no intention of
> using older code (once I have one version of Python covered, then I'll
> look into making code that's compatible with 2.x if I have to).

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Re: Access violation reading 0x00000010

[yuan zheng]

I have found my question's answer. The fault is sourced
from the implement of SIM_init().


Thanks a lot.



thanks,
yuanzheng.

2011/4/28 yuan zheng 

> Sorry , the path is just an example.
>
> This is not the question I think. Because there is lots of api
> in libcommon-0.dll, and there is no fault when invoking other
> api, such as libcommon.SIM_start().. It's just fault when invoking
> this api -> SIM_init(). So I wanna which situation would lead to this
> error:
>
> --
>
> WindowsError: exception: access violation reading 0x0010
>
> --
>
>
>
> thanks,
> yuanzheng.
>
>
> 2011/4/28 Chris Angelico 
>
>> On Thu, Apr 28, 2011 at 4:01 PM, yuan zheng 
>> wrote:
>> >
>> > libcommon = CDLL("c:\libcommon-0.dll", RTLD_GLOBAL)
>> >
>> > libcommon.SIM_init() -> This is the invoking.
>>
>> When you have a backslash in a literal string, you need to double it:
>> libcommon = CDLL("c:\\libcommon-0.dll", RTLD_GLOBAL)
>>
>> I don't know if that's your problem, but it could be!
>>
>> Chris Angelico
>> --
>> http://mail.python.org/mailman/listinfo/python-list
>>
>
>
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Re: unpickling derived LogRecord in python 2.7 from python2.6

[Peter Otten]

Vinay Sajip wrote:

> On Apr 27, 5:41 pm, Peter Otten <__pete...@web.de> wrote:
> 
>> The Problem is that as of Python 2.7logging.LogRecord has become a
>> newstyle class which is pickled/unpickled differently. I don't know if
>> there is an official way to do the conversion, but here's what I've
>> hacked up. The script can read pickles written with 2.6 in 2.7, but not
>> the other way round.
>> [code snipped]
> 
> I don't know about "official", but another way of doing this is to
> pickle just the LogRecord's __dict__ and send that over the wire. The
> logging package contains a function makeLogRecord(d) where d is a
> dict.

You are right, my approach is too complicated and only needed when the OP 
cannot modify the sending script -- which is unlikely.

> This is the approach used by the examples in the library documentation
> which pickle events for sending across a network:
> 
> http://docs.python.org/howto/logging-cookbook.html#sending-and-receiving-
logging-events-across-a-network
> 
> The built-in SocketHandler pickles the LogRecord's __dict__ rather
> than the LogRecord itself, precisely because of the improved
> interoperability over pickling the instance directly.

As a minimal change ensuring that the logging.LogRecord subclass used by the 
OP is a newstyle class in 2.6 with

class LogRecord(logging.LogRecord, object):
#...

should work, too.
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argparse parser stores lists instead of strings

[Andrew Berg]

I've set up groups of arguments for a script I'm writing, and any time I
give an argument a value, it gets stored as a list instead of a string,
even if I explicitly tell it to store a string. Arguments declared with
other types (e.g. float, int) and default values are stored as expected.
For example:

vidin_args=parser.add_argument_group('Video Input Options', 'Various
options that control how the video file is demuxed/decoded.')
vidin_args.add_argument('-m', dest='vmode', nargs=1, type=str,
metavar='video_mode', choices=['ntsc', 'pal', 'film', 'ivtc'],
default='ntsc', help='Valid values are "ntsc", "pal", "film" and "ivtc".')
...more arguments...
opts=parser.parse_args()

If I assign a value on the command line (e.g. -m pal), opts.vmode is a
list, otherwise it's a string. This is pretty bad since I can't know
whether to get opts.vmode or opts.vmode[0] later in the script. I could
loop through all the options and convert each option to a string, but
that's not really something I want to do, especially if I start adding
more options.

I'm pretty new to Python, and I might have missed something, but I have
been looking!
In case it matters, I'm learning Python 3.2 and have no intention of
using older code (once I have one version of Python covered, then I'll
look into making code that's compatible with 2.x if I have to).
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Re: Reliably call code after object no longer exists or is "unreachable"?

[Gregory Ewing]

Jack Bates wrote:


Python's __del__ or destructor method works (above) - but only in the
absence of reference cycles (below). An object, with a __del__ method,
in a reference cycle, causes all objects in the cycle to be
"uncollectable".


Store a weak reference to the object somewhere with a
callback. This should work even in the presence of
cycles, as long as the weak reference itself isn't
part of the cycle.

--
Greg
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Re: Have you read the Python docs lately?

[Terry Reedy]

On 4/27/2011 7:40 PM, Ben Finney wrote:

http://docs.python.org/dev/howto/logging.html


This one in particular was sorely needed, especially its early if-then
discussion of whether to use ‘logging’ at all. Thanks very much to Vinay
Sajip.


Yes, he has been working pretty steadily for some months to improve the 
tests, code, and docs.


--
Terry Jan Reedy


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