Re: [Tutor] pandas data frame

[Bachir Bachir via Tutor]

 Hi Peter Thank you much for your help its very appreciated ,bellow is an 
example of what i need.   The main dataframe ( need to be separated into 
separate dataframes  ). The desired dataframes output correctly as i need it to 
be,Thanks much
Main dataframendx     V_id        Average        Mean       Peak 0         1    
          3                      2          51         2              2         
             1          62         3              4                     1       
   83         1              2                      2          74         2     
         3                     3          65         3              5           
          3          46         1              1                     1          
87         2              2                     5          108         3        
      5                     5          99         1              2              
       5          1010        2             5                     5          
911        3             4                     3          10
Dataframe-1ndx     V_id   Average     Mean    Peak 0         1           3      
        2          53         1           2              2          76         
1           1              1          89         1           2              5   
       10
Dataframe-2ndx     V_id    Averag    Mean     Peak 1          2           2     
         1          64          2           3              3          67        
  2           2              5          1010        2           5              
5          9
Dataframe-3ndx     V_id    Average    Mean    Peak 2         3           4      
        1          85         3           5              3          48         
3           5              5          911        3           4              3   
       10
Bachir

 

On Monday, January 18, 2016 11:25 AM, Peter Otten <__pete...@web.de> wrote:
 

 Bachir Bachir wrote:

[Bachir, please send your mails to the list, not to me. That way you 
increase the likelihood to get a good answer]

>>    On Sunday, January 17, 2016 4:20 PM, Peter Otten <__pete...@web.de>
>> wrote:
>>  Bachir Bachir via Tutor wrote:
>>> Hello EverybodyI need to sort a dataframe according to a specific column
>>> the create new dataframes according to the sorted columns each new
>>> created dataframe should contain the list(set('the sorted element)any
>>> help please, i am new in python and pandas thanks muchBachir
>> 
>> Like this?
>> 
>> >>> df
>> 
>>  foo bar
>> 0  3.3  b
>> 1  2.2  b
>> 2  7.5  a
>> 3  1.1  c
>> 4  4.7  a
>> 
>> [5 rows x 2 columns]
>> 
>> >>> df.groupby("bar").sum()
>> 
>>      foo
>> bar    
>> a    12.2
>> b    5.5
>> c    1.1
>> 
>> [3 rows x 1 columns]

> Thanks Peter ,This way but i  want keep all the table elements only
> separate them  by a single column 

I'm sorry, I don't understand what you mean by "separate them by a single 
column". Can you give an example? What exactly should the sorted version of

>> >>> df
>> 
>>  foo bar
>> 0  3.3  b
>> 1  2.2  b
>> 2  7.5  a
>> 3  1.1  c
>> 4  4.7  a
>> 
>> [5 rows x 2 columns]

look like?

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[Tutor] Fwd:

[Deepak Nn]

-- Forwarded message --
From: Deepak Nn 
Date: Mon, Jan 18, 2016 at 6:27 PM
Subject: Re:
To: tutor-ow...@python.org


Please provide a python program to run a program (.exe) and get Hash
*exactly* as :

 160 106 182 190 228 64 68 207 248 109 67 88 41 .The username to be
used is admin
.The *password* is what to be found out .The hash provided is of the
correct password .Mostly the password will be *13 char long *and has a
small chance of being all alpha characters .*GOOGLE DOES NOT ALLOW TO SENT
.EXE FILE .*

Provide the where is change i have to make in the program to run the .exe
file that i have in my computer .

Since i can't sent the .exe file .i am sending the screen shorts of the
program .*The text file of the program is included and few screenshots of
 the the the result of the program is also included* .
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Re: [Tutor] str.strip strange result...?

[Albert-Jan Roskam]

 
> From: d...@hashcollision.org
> Date: Mon, 18 Jan 2016 00:29:41 -0800
> Subject: Re: [Tutor] str.strip strange result...?
> To: sjeik_ap...@hotmail.com
> CC: __pete...@web.de; tutor@python.org
> 
> > Not sure which one is faster, but in this case I actually find a regex more 
> > readable (!):
>  re.sub(r"_1$", "", "V01_1")
> > 'V01'
> 
> 
> Hi Albert-Jan Roskam,
> 
> Here's a minor counterpoint to using regexes here: they're sometimes a
> bit too powerful. Yes, certainly: https://xkcd.com/208/ :-)
> 
> In this situation, a regex approach might be troublesome if parts of
> the suffix can be interpreted as regular expression meta-characters.
> For example, if we were trying to strip out a suffix like
> 
> ".exe"
> 
> then if we were to try to do this with regexes, we might forget that
> "." is a meta-character that acts as a wildcard for any single
> character.  Therefore, a regexp-based solution for the general
> suffix-removal problem is complicated because we'd need consider
> escaping certain characters.  Not that this would be hard, but that
> it's yet another detail we have to keep in our heads.
Agreed. Apart from backslashes, re.escape could also be really handy. But 
regexes are scary and intimidating for those who have never seen them before.
> Another disadvantage is that, if the suffix is dynamically determined,
> then there's an additional cost in "compiling" the regular expression:
> building the pattern-matching machinery doesn't come for free.
re.compile helps, though it always bothers me that I "need" to put them as a 
global in the top-level of my module (along with collections.namedtuple).Unless 
I use a class, where __init__ is a good place.
 
> For those reasons, I think the regexp approach here is a little bit of
> overkill.  This kind of tradeoff is the sort of thing that reference
> documentation will probably not mention.   That's why this list is
> here, to share the experience of using these systems with other
> beginners and learners.  Regexes are still very useful: just be aware
> that they have sharp edges.
 One other downside is that it takes only a couple of days/beers before one 
forgets the regex. But re.VERBOSE and named groups help a LOT.
 
> Good luck to you!
  
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Re: [Tutor] str.strip strange result...?

[Danny Yoo]

> Not sure which one is faster, but in this case I actually find a regex more 
> readable (!):
 re.sub(r"_1$", "", "V01_1")
> 'V01'


Hi Albert-Jan Roskam,

Here's a minor counterpoint to using regexes here: they're sometimes a
bit too powerful.

In this situation, a regex approach might be troublesome if parts of
the suffix can be interpreted as regular expression meta-characters.
For example, if we were trying to strip out a suffix like

".exe"

then if we were to try to do this with regexes, we might forget that
"." is a meta-character that acts as a wildcard for any single
character.  Therefore, a regexp-based solution for the general
suffix-removal problem is complicated because we'd need consider
escaping certain characters.  Not that this would be hard, but that
it's yet another detail we have to keep in our heads.

Another disadvantage is that, if the suffix is dynamically determined,
then there's an additional cost in "compiling" the regular expression:
building the pattern-matching machinery doesn't come for free.


For those reasons, I think the regexp approach here is a little bit of
overkill.  This kind of tradeoff is the sort of thing that reference
documentation will probably not mention.   That's why this list is
here, to share the experience of using these systems with other
beginners and learners.  Regexes are still very useful: just be aware
that they have sharp edges.


Good luck to you!
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Re: [Tutor] if request.method == 'GET': NameError: global name 'request' is not defined

[sudipto manna]

Here is the code snippet:

File#FlaskTest2.py

from flask import Flask

app = Flask(__name__)

#Make an app.route() decorator here
@app.route("/puppies/", methods = ['GET' , 'POST'])
def puppiesFunction():
  if request.method == 'GET':
  return getAllPuppies()

  elif request.method == 'POST':
   return makeANewPuppy()

File# FlaskTendpointTester2.py
import httplib2
import json
import sys

print "Running Endpoint Tester\n"
address = raw_input("Please enter the address of the server you want to
access, \n If left blank the connection will be set to '
http://localhost:5000':   ")
if address == '':
address = 'http://localhost:5000'
#Making a GET Request
print "Making a GET Request for /puppies..."

Virtual machine is running on port:5000

and the error trace seen on when the endpoint code is executed on localhost
port:5000

Traceback (most recent call last):

  File
"/Users/sudiptomanna/anaconda2/lib/python2.7/site-packages/flask/app.py",
line 1836, in __call__

return self.wsgi_app(environ, start_response)

  File
"/Users/sudiptomanna/anaconda2/lib/python2.7/site-packages/flask/app.py",
line 1820, in wsgi_app

response = self.make_response(self.handle_exception(e))

  File
"/Users/sudiptomanna/anaconda2/lib/python2.7/site-packages/flask/app.py",
line 1403, in handle_exception

reraise(exc_type, exc_value, tb)

  File
"/Users/sudiptomanna/anaconda2/lib/python2.7/site-packages/flask/app.py",
line 1817, in wsgi_app

response = self.full_dispatch_request()

  File
"/Users/sudiptomanna/anaconda2/lib/python2.7/site-packages/flask/app.py",
line 1477, in full_dispatch_request

rv = self.handle_user_exception(e)

  File
"/Users/sudiptomanna/anaconda2/lib/python2.7/site-packages/flask/app.py",
line 1381, in handle_user_exception

reraise(exc_type, exc_value, tb)

  File
"/Users/sudiptomanna/anaconda2/lib/python2.7/site-packages/flask/app.py",
line 1475, in full_dispatch_request

rv = self.dispatch_request()

  File
"/Users/sudiptomanna/anaconda2/lib/python2.7/site-packages/flask/app.py",
line 1461, in dispatch_request

return self.view_functions[rule.endpoint](**req.view_args)

  File "/Users/sudiptomanna/fullstack/vagrant/PythonData/FlaskTest2.py",
line 8, in puppiesFunction

if request.method == 'GET':

NameError: global name 'request' is not defined


Regards,

Sudipto Manna

On Sun, Jan 17, 2016 at 7:17 PM, Alan Gauld 
wrote:

> On 17/01/16 23:15, sudipto manna wrote:
> > Hi All,
> > I am running a python flask project for fetching the endpoint.
> >
> > Please find the files attached.
>
> OK, This is a text based mailing list so attachments tend
> not to make it through the server. If they are not too long post them
> here, or if they are bigger put them on a pastebin. However...
>
> Flask is not part of the standard library so a little bit
> off topic for this list, you may be better off asking on
> the Flask support forum.
>
> Howe er it is a common framework so somebody here might
> be able to help.
>
> > When the endpoint file is executed its returning this error:
> > "if request.method == 'GET': NameError: global name 'request' is not
> > defined"
>
> We really need to see the full error trace and the full
> context around the reported fault - ideally the full file.
> The probability is that the error is telling the truth
> and 'request' is not defined yet. Is it part of Flask?
> Should you have prepended the module name?
> Is the spelling/case correct?
>
>
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.amazon.com/author/alan_gauld
> Follow my photo-blog on Flickr at:
> http://www.flickr.com/photos/alangauldphotos
>
>
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Re: [Tutor] if request.method == 'GET': NameError: global name 'request' is not defined

[Danny Yoo]

On Sun, Jan 17, 2016 at 6:13 PM, sudipto manna  wrote:
> Here is the code snippet:
>
> File#FlaskTest2.py
>
> from flask import Flask
>
> app = Flask(__name__)
>
> #Make an app.route() decorator here
> @app.route("/puppies/", methods = ['GET' , 'POST'])
> def puppiesFunction():
>   if request.method == 'GET':
>   return getAllPuppies()


Hi Sudipto,

I don't know the Flask framework here, but this code looks suspicious.
What is "request" in this puppiesFunction definition?  It's not a
parameter.  Where does it come from?

Is it a global?

http://flask.pocoo.org/docs/0.10/quickstart/#accessing-request-data

... oh.  It is a module global.  That is not something I like
philosophically, but oh well, roll with it...


Do you have other working examples from prior code that used requests?
 If so, you may want to double check them.  You're missing a
definition that you need to add to your program.  Take a look at the
documentation: read the "The Request Object" section in the docs, and
you should see the missing line that you need to add to your program.


If you can't find it after you've read this quickstart documentation,
please feel free to ask the mailing list.  But you should be able to
see it: it's the first boxed piece of code at:

http://flask.pocoo.org/docs/0.10/quickstart/#the-request-object


Good luck!
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Re: [Tutor] if request.method == 'GET': NameError: global name 'request' is not defined

[Alan Gauld]

On 18/01/16 02:13, sudipto manna wrote:
> Here is the code snippet:
>
> File#FlaskTest2.py
>
> from flask import Flask
>
> app = Flask(__name__)
>
> #Make an app.route() decorator here
> @app.route("/puppies/", methods = ['GET' , 'POST'])
> def puppiesFunction():
>   if request.method == 'GET':
>   return getAllPuppies()
>
As suspected the error is correct. You do not have a request object
anywhere in your code. A quick Google tells me that it is part
of Flask. So you need to import request from your flask module:

from flask import Flask, request,,# any other names you use

hth

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos

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Re: [Tutor] if request.method == 'GET': NameError: global name 'request' is not defined

[Cameron Simpson]

On 17Jan2016 20:13, sudipto manna  wrote:

Here is the code snippet:

File#FlaskTest2.py

from flask import Flask


You need to import "request" from flask as well:

 from flask import Flask, request

For others on this list: the Flask framework presents the current web request 
as a thread local global called "request"; simplifies writing handlers as the 
request information is readily available without having to pass it through 
function calls.


Cheers,
Cameron Simpson 
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Re: [Tutor] pandas data frame

[Peter Otten]

Bachir Bachir wrote:

[Bachir, please send your mails to the list, not to me. That way you 
increase the likelihood to get a good answer]

>> On Sunday, January 17, 2016 4:20 PM, Peter Otten <__pete...@web.de>
>> wrote:
>>  Bachir Bachir via Tutor wrote:
>>> Hello EverybodyI need to sort a dataframe according to a specific column
>>> the create new dataframes according to the sorted columns each new
>>> created dataframe should contain the list(set('the sorted element)any
>>> help please, i am new in python and pandas thanks muchBachir
>> 
>> Like this?
>> 
>> >>> df
>> 
>>   foo bar
>> 0  3.3  b
>> 1  2.2  b
>> 2  7.5  a
>> 3  1.1  c
>> 4  4.7  a
>> 
>> [5 rows x 2 columns]
>> 
>> >>> df.groupby("bar").sum()
>> 
>>   foo
>> bar 
>> a12.2
>> b5.5
>> c1.1
>> 
>> [3 rows x 1 columns]

> Thanks Peter ,This way but i  want keep all the table elements only
> separate them  by a single column 

I'm sorry, I don't understand what you mean by "separate them by a single 
column". Can you give an example? What exactly should the sorted version of

>> >>> df
>> 
>>   foo bar
>> 0  3.3  b
>> 1  2.2  b
>> 2  7.5  a
>> 3  1.1  c
>> 4  4.7  a
>> 
>> [5 rows x 2 columns]

look like?

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Re: [Tutor] if request.method == 'GET': NameError: global name 'request' is not defined

[Danny Yoo]

On Mon, Jan 18, 2016 at 7:59 AM, sudipto manna  wrote:
> Thanks All.
> The import request was missing and the issue was resolved upon calling that
> module and initializing it.


Hi Sudipto Manna,


One last thing before you go on.  Do a small retrospective: now that
you know why things weren't working, look back at the original error
message again.


###
 File "/Users/sudiptomanna/fullstack/vagrant/PythonData/FlaskTest2.py",
line 8, in puppiesFunction

if request.method == 'GET':

NameError: global name 'request' is not defined
###


Does the message in the error message make more sense to you now?



Best of wishes!
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Re: [Tutor] Should a "data" directory have a __init__.py file?

[Oscar Benjamin]

On 18 January 2016 at 04:27, Ben Finney  wrote:
>
> The module import system will only recognise a directory as a “package”
> (Python's technical term for “a point in the import hierarchy which
> contains other things to import”) if that directory contains a file
> named ‘__init__.py’. If you do not need the directory to also be
> recognised as a package, it should not have such a file.

That was the case prior to 3.3. However (I can't immediately test this
but) now a directory without an __init__.py can be an implicit
namespace package if it contains importable modules:

https://www.python.org/dev/peps/pep-0420/

--
Oscar
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Re: [Tutor] How (and whether I should) use pkgutil.get_data()?

[Oscar Benjamin]

On 17 January 2016 at 23:37, boB Stepp  wrote:
> 1)  Is using pkgutil.get_data() the way I should be reading my data files?

Generally yes, although it may be unnecessary. The main purpose of
pkgutil.get_data is to transparently handle the case where your
packages are imported from a zip file. The initial motivation for this
was setuptools eggs but there are other reasons you might want to
import your code from a zip file.

> 2)  The book says that this method will return "...a byte string
> containing the raw contents of the file." (From page 409) Can I do all
> of the normal things on this returned object that I could do if I used
> "with open..."?  Is it iterable?  [OK, I confess up front.  I am being
> lazy here.  I *could* create a file and try this out to see what
> happens, so I will understand if I get chided (or worse!).]

Just try it out :)

> 3)  Should I be using relative imports in my projects?

I don't use relative imports. The supposed advantage of relative
imports is that you can easily move a package to a different location
in the import hierarchy. For example if you have a package called
stuff and the modules inside stuff use relative imports to access each
other then you could move stuff inside another package called things
and have it be a package called things.stuff without needing to change
the import lines.

Personally I think that fixing up a few import lines is no big deal.
I'd rather choose exactly where things is going to go in the import
hierarchy and be done with it. If I need to move it into another
package then I'll have to change the import statements inside things
but that's easy to do. So I prefer absolute imports since they're less
ambiguous.

--
Oscar
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Re: [Tutor] if request.method == 'GET': NameError: global name 'request' is not defined

[sudipto manna]

Thanks All.
The import request was missing and the issue was resolved upon calling that
module and initializing it.

Thanks for the guidance.

Regards,
Sudipto Manna

On Mon, Jan 18, 2016 at 3:55 AM, Cameron Simpson  wrote:

> On 17Jan2016 20:13, sudipto manna  wrote:
>
>> Here is the code snippet:
>>
>> File#FlaskTest2.py
>>
>> from flask import Flask
>>
>
> You need to import "request" from flask as well:
>
>  from flask import Flask, request
>
> For others on this list: the Flask framework presents the current web
> request as a thread local global called "request"; simplifies writing
> handlers as the request information is readily available without having to
> pass it through function calls.
>
> Cheers,
> Cameron Simpson 
>
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[Tutor] Password decoding (was Re: Fwd:)

[Alan Gauld]

On 18/01/16 13:06, Deepak Nn wrote:

> Please provide a python program to run a program (.exe) and get Hash
> *exactly* as :
> 
>  160 106 182 190 228 64 68 207 248 109 67 88 41 .The username to be
> used is admin
> .The *password* is what to be found out .The hash provided is of the
> correct password .Mostly the password will be *13 char long *and has a
> small chance of being all alpha characters .*GOOGLE DOES NOT ALLOW TO SENT
> .EXE FILE .*
> 
> Provide the where is change i have to make in the program to run the .exe
> file that i have in my computer .
> 
> Since i can't sent the .exe file .i am sending the screen shorts of the
> program .*The text file of the program is included and few screenshots of
>  the the the result of the program is also included* .

The list server does not generally let attachments through.

Also, we will not do your homework for you, although we
will try to help you do it. Please show us what you have
tried so far and any error messages (in full).

Ask specific questions and you will get specific help.

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos


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Re: [Tutor] Simultaneous read and write on file

[Alan Gauld]

On 18/01/16 16:01, Anshu Kumar wrote:
> Hello Everyone,
> 
> I try below code in python 2.7.10 to first create and write into a file and
> then read and write that file but what i get is just a  file with new
> content.
> 
> 
 with open('test.txt', 'wb+') as f:
> ... f.write('this is test file.')
> ... f.write('ok!!!')
> ...
 with open('test.txt', 'wb+') as f:
> ... a_str = f.read() + 'read the file'
> ... f.seek(0)
> ... f.write(a_str)
> ...

You called f.seek(0) which puts the cursor right back to the start
of the file. Try writing without using the f.seek().

But since you only want to append, it would be better and safer to use
append mode instead.

The + modes are deceptively appealing but they are full of dangers
for precisely the reasons you have discovered(*). You very rarely
need them and you are better opening/closing the file and
using explicit modes to read/write.

(*)Another problem, apart from the risks of overwriting your
data,  is that the + modes will lock the file even while you
are just reading it, which might cause a problem with shared
files)

> I have read in documentation that wb+ mode is for writing and reading. Am i
> using wrong mode, should i use rb+ ?

No, you should probably be separately using 'r' to read and 'a'
to append.

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos


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[Tutor] Simultaneous read and write on file

[Anshu Kumar]

Hello Everyone,

I try below code in python 2.7.10 to first create and write into a file and
then read and write that file but what i get is just a  file with new
content.


>>> with open('test.txt', 'wb+') as f:
... f.write('this is test file.')
... f.write('ok!!!')
...
>>> with open('test.txt', 'wb+') as f:
... a_str = f.read() + 'read the file'
... f.seek(0)
... f.write(a_str)
...


I have read in documentation that wb+ mode is for writing and reading. Am i
using wrong mode, should i use rb+ ?

Thanks and regards,
Anshu
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Re: [Tutor] Fwd:

[Danny Yoo]

> Please provide a python program to run a program (.exe) and get Hash
> *exactly* as :
>
>  160 106 182 190 228 64 68 207 248 109 67 88 41 .The username to be
> used is admin
> .The *password* is what to be found out .The hash provided is of the
> correct password .Mostly the password will be *13 char long *and has a
> small chance of being all alpha characters .


Hi Deepak,

This doesn't seem like a beginner-level question.  If I had a guess,
it sounds more like something out of a shady rent-a-coder kind of
thing.

Unfortunately, I don't think we can help with this.  Even if we did
have the technical expertise, I still don't think we should help on
this in the first place.  If I'm understanding the question correctly,
you're asking for brute password breaking, which goes against most
professional codes of conduct.  Example:
https://www.acm.org/about-acm/acm-code-of-ethics-and-professional-conduct.
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Re: [Tutor] An Advice to a dedicated beginner

[Alan Gauld]

On 19/01/16 01:15, Michael Appiah Boachie wrote:
> I am a programming beginner. ...
> when i sat on my own with a couple of materials and videos,
> I have become very good at the basics of python and
> completing various beginner courses and projects with ease 
> but however I have run into some kind of “beginner wall”
> where I don’t know where or what to take on next.

The first thing to do is to find a concept or project
that you want to build. We can't really help you with
that, it has to come from you. But maybe there is a
routine task you perform that you could automate?

Say, renaming photos that you load from a camera?
Or bulk conversion of music files between formats?
Or you have a spreadsheet with some macros that you
could convert to an application, maybe using a database?
Or maybe it's a game that you like? Or you could
generate reports from some data source? Maybe from
a web site?

Once you have a project, you need to decide how to build
it, and what modules you will be using.


That second action is where my last book comes in.
Python Projects is targeted at people like you, who know
the basic language, but now want to do something with it.
It covers: interacting with the OS, managing data,
building UIs and web sites and using the Python
test tools.

I try to avoid too much self promotion on this list
but it does sound like you might benefit from this one.


What it doesn't cover much is how to design a program,
that's a much more abstract concept and there are
whole books on that topic. But, for a beginners project,
it shouldn't be a huge issue, the important thing
is to pick something and make a start.

If you get stuck come back here.


-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos


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[Tutor] An Advice to a dedicated beginner

[Michael Appiah Boachie]

Hello Tutors,

I am a programming beginner. Throughout college, I have not properly grasp 
anything the professor’s teach but when i sat on my own with a couple of 
materials and videos, I have become very good at the basics of python and 
completing various beginner courses and projects with ease but however I have 
run into some kind of “beginner wall” where I don’t know where or what to take 
on next. This is killing my excitement. I think this isn’t something new to 
experienced programmers to hear. That’s why I am asking for help. Please any 
advice would help a dedicated one here. I don’t know what to do next with the 
knowledge I have acquired. People keep saying “get into open source” , “do that 
and that”. I wish they actually knew how someone like me feel. There are so 
many videos, articles and materials to get you to know basics and also become a 
top expert but almost nothing on how to transition into that. That’s exactly 
how I’m feeling. 

Hoping to receive some kind words.

Michael
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Re: [Tutor] An Advice to a dedicated beginner

[Ben Finney]

Alan Gauld  writes:

> On 19/01/16 01:15, Michael Appiah Boachie wrote:
> > I am a programming beginner. ...
> > when i sat on my own with a couple of materials and videos,
> > I have become very good at the basics of python and
> > completing various beginner courses and projects with ease 
> > but however I have run into some kind of “beginner wall”
> > where I don’t know where or what to take on next.
>
> The first thing to do is to find a concept or project
> that you want to build. We can't really help you with
> that, it has to come from you. But maybe there is a
> routine task you perform that you could automate?

That's a worthwhile recommendation.

I usually recommend something different: Pick an *existing* code base
that you're already using – Python is used in a great many tools that
you probably rely on, so this shouldn't be difficult – and get the
source code. Find small improvements to make, discuss them with peers
and on this forum, and with the developers of that code base.

Making small improvements to something you already use will avoid the
“blank slate” paralysis from having too many options be motivational,
while also being very motivational: you already can think of
improvements you would like to make, and getting them implemented will
be very satisfying.

It also focusses on an often-dismissed aspect of learning to program:
you need to program *with other people*, and your code is a means of
communicating with those people. Learning how to do that, and learning
(by doing) that there is no shame in starting small and unskilled, is a
necessary part of the craft.

-- 
 \   “The long-term solution to mountains of waste is not more |
  `\  landfill sites but fewer shopping centres.” —Clive Hamilton, |
_o__)_Affluenza_, 2005 |
Ben Finney

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Re: [Tutor] Simultaneous read and write on file

[Martin A. Brown]

Hello,

>> I have read in documentation that wb+ mode is for writing and 
>> reading. Am i using wrong mode, should i use rb+ ?
>
>Use w+ to create a new file, opened with read and write access. Use 
>r+ to open an existing file with read and write access. Unlike w+, 
>r+ does not truncate the file and will not create a new file.

[snip]

>FYI, in terms of POSIX open flags [1], the file mode gets mapped as follows:
>
>  |   flags   |   no +   |   +
>-
>r |   | O_RDONLY | O_RDWR
>w | O_CREAT, O_TRUNC  | O_WRONLY | O_RDWR
>a | O_CREAT, O_APPEND | O_WRONLY | O_RDWR
>
>Python 3 only:
>
>x | O_CREAT, O_EXCL   | O_WRONLY | O_RDWR
>
>In terms of Windows open dispositions and access modes [2], the file
>mode gets mapped as follows:
>
>  |  disposition  |  no + |+
>---
>r | OPEN_EXISTING | GENERIC_READ  | GENERIC_READ, GENERIC_WRITE
>w | CREATE_ALWAYS | GENERIC_WRITE | GENERIC_READ, GENERIC_WRITE
>a | OPEN_ALWAYS   | GENERIC_WRITE | GENERIC_READ, GENERIC_WRITE
>
>Python 3 only:
>
>x | CREATE_NEW| GENERIC_WRITE | GENERIC_READ, GENERIC_WRITE

The above is a very handy chart.  Did you find this somewhere, eryk 
sun, or is this from your own knowledge and experience?  This might 
benefit an experienced Windows/POSIX user trying to understand 
open() in Python if it were available in the standard documentation.

Thanks for mapping this to common operating systems.  I had inferred 
this already, but this is a great summary.

-Martin

-- 
Martin A. Brown
http://linux-ip.net/
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Re: [Tutor] Simultaneous read and write on file

[Cameron Simpson]

On 18Jan2016 20:41, Martin A. Brown  wrote:

Yes and so have I. Maybe twice in 30 years of programming. [...]


I may have done it a little more than that; I agree it is very
rare. I may be biased because I was debugging exactly this last
week. (Which itself is an argument against mixed rerad/write with
one file - it was all my own code and I spent over a day chasing
this because I was looking in the wrong spot).


Oh yes.  Ooof.  Today's decisions are tomorrow's albatross.


Actually I have good reason to mix these in this instance, and now that it is 
debugged it is reliable and more efficient to boot.


[...]

Tip for new players: if you do any .write()s, remember to do a
.flush() before doing a seek or a read


That's exactly my point. There are so many things you have to do
extra when working in mixed mode. Too easy to treat things like
normal mode files and get it wrong. Experts can do it and make it
work, but mostly it's just not needed.


Yes. You're write - for simplicity and reliability two distinct
open file instances are much easier.


Yes, he's write [sic].  He writes a bunch!  ;)


Alas, I have a tendency to substitute homophones, or near homophones, when 
typing in a hurry. You'll see this in a bunch of my messages. More annoyingly, 
some are only visible when I reread a posted message instead of when I was 
proofreading prior to send.



[Homonyms mess me up when I'm typing, all sew.]


Homonyms too.

Cheers,
Cameron Simpson 
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Re: [Tutor] Simultaneous read and write on file

[Cameron Simpson]

On 18Jan2016 21:07, ALAN GAULD  wrote:

On 18/01/16 20:43, Cameron Simpson wrote:

The + modes are deceptively appealing but they are full of dangers
for precisely the reasons you have discovered(*). You very rarely
need them and you are better opening/closing the file and
using explicit modes to read/write.


But if he wants to mix the modes, he certainly should be experimenting. Having
a file open for read and write is sometimes useful; I do it myself in certain
circumstances.


Yes and so have I. Maybe twice in 30 years of programming.
It's sometimes necessary but it's much, much harder to get
right and very easy to get wrong, usually with data corruption
as a result.


I may have done it a little more than that; I agree it is very rare. I may be 
biased because I was debugging exactly this last week. (Which itself is an 
argument against mixed rerad/write with one file - it was all my own code and I 
spent over a day chasing this because I was looking in the wrong spot).



So for a beginner I would never encourage it. For an
experienced programmer sure' if there is no other option
(and especially if you have fixed size records where
things get easier).


Tip for new players: if you do any .write()s, remember to do a .flush() before
doing a seek or a read


That's exactly my point. There are so many things you have
to do extra when working in mixed mode. Too easy to treat
things like normal mode files and get it wrong. Experts
can do it and make it work, but mostly it's just not needed.


Yes. You're write - for simplicity and reliability two distinct open file 
instances are much easier.



Disagree. As far as his question goes, "wb+" is a correct mode for what he is
trying. Whether it is a sensible approach depends very much on what he is doing
with his files.


I'm not sure we know what he(?) is trying.
We only know he successfully overwrote his data and
that apparently was not his intention. There are use
cases where it makes sense but in most cases you can
get by just fine without.


Yeah. I think I was more narked by your not answering his "is wb+ correct" 
literally; it may be only rarely the reasonable course, but for what he was 
actually _asking_ wb+ is correct. He may not be doing the best design but as 
you say we don't know his actual use case.


For the narkiness I apologise.

Cheers,
Cameron Simpson 
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Re: [Tutor] Simultaneous read and write on file

[Cameron Simpson]

On 18Jan2016 22:29, Peter Otten <__pete...@web.de> wrote:

Anshu Kumar wrote:

I have read in documentation that wb+ mode is for writing and reading. Am
i using wrong mode, should i use rb+ ?


Quoting https://docs.python.org/2.7/library/functions.html#open
"""
note that 'w+' truncates the file.
"""
That's why you lose the file's current content, and, yes, "r+b" would avoid
that.


And I stand corrected; I should have paid more attention. Thanks!

Cheers,
Cameron Simpson 
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Re: [Tutor] Simultaneous read and write on file

[Martin A. Brown]

Hi all,

 The + modes are deceptively appealing but they are full of dangers
 for precisely the reasons you have discovered(*).
>
>> Yes and so have I. Maybe twice in 30 years of programming. It's 
>> sometimes necessary but it's much, much harder to get right and 
>> very easy to get wrong, usually with data corruption as a result.

Yes.
Yes.
Yes.
Yes.
Yes.

> I may have done it a little more than that; I agree it is very 
> rare. I may be biased because I was debugging exactly this last 
> week. (Which itself is an argument against mixed rerad/write with 
> one file - it was all my own code and I spent over a day chasing 
> this because I was looking in the wrong spot).

Oh yes.  Ooof.  Today's decisions are tomorrow's albatross.

Speaking of which, I have an albatross in very good condition and 
I'm looking for a buyer.  Anybody interested in a short-tailed 
albatross with good manners.  Looking for a good home.

>> So for a beginner I would never encourage it. For an experienced 
>> programmer sure' if there is no other option (and especially if 
>> you have fixed size records where things get easier).
>>
>>> Tip for new players: if you do any .write()s, remember to do a 
>>> .flush() before doing a seek or a read
>>
>> That's exactly my point. There are so many things you have to do 
>> extra when working in mixed mode. Too easy to treat things like 
>> normal mode files and get it wrong. Experts can do it and make it 
>> work, but mostly it's just not needed.
>
> Yes. You're write - for simplicity and reliability two distinct 
> open file instances are much easier.

Yes, he's write [sic].  He writes a bunch!  ;)

[Homonyms mess me up when I'm typing, all sew.]

OK, a bit more seriously, I will add a thought or two.

Modern filesystems are beautiful.  They are fast, reliable and 
efficient.  Application software, e.g. Python, can be hairy (see the 
points of Alan and Cameron earlier in this thread).  Why not take 
advantage of filesystem atomicity, a feature guarantee to userspace 
from all (?) modern local filesystems.

Options:

  * If disk throughput is not a problem, then there's practically 
nothing but a benefit to reading from input file, writing to 
output file, closing both and renaming (effectively squashing 
the original file)

  import os
  A = open('a', 'w')
  A.write('hammy')
  A.close()
  A = open('a', 'r')
  B = open('b', 'w')
  data = A.read() # -- processing handled
  data = data.replace('m', 'p')   #here, until happy
  B.write(data)
  B.close()
  A.close()
  os.rename(B.name, A.name)   # -- atomic [0]

  * Alternative:  If disk throughput is a problem, this is an 
argument for using a database system where this class of data 
integrity problem has been solved for the application 
developer.

I'd suggest measuring the amount of time it takes to read, rewrite 
and os.rename() the entire file before deciding you need to 
undertake the massive complexity of modifying an existing file in 
situ.

If you can avoid modifying an existing file, don't bother with it. 
You will likely bring yourself (and maybe even others) headache.  

For example, if another reader of the file comes along while you are 
performing your in situ modification magic tricks, they (and you) 
will have no guarantees about what data they will receive.  That 
will be left up to the operating system (i.e. kernel).

So, take control of the data back into your own hands by taking 
adavantage of the beauty of the filesystem.

Filesystem atomicity!

Good luck,

-Martin

 [0] Or just about as close as conceivably possible to atomic as you 
 can be guaranteed in userspace applications.

-- 
Martin A. Brown
http://linux-ip.net/
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[Tutor] Beautiful Soup

[Crusier]

Hi Python Tutors,

I am currently able to strip down to the string I want. However, I
have problems with the JSON script and I am not sure how to slice it
into a dictionary.

import urllib
import json
import requests

from bs4 import BeautifulSoup


url = 
'https://bochk.etnet.com.hk/content/bochkweb/eng/quote_transaction_daily_history.php?code=6881\
=F=09=16=S=44c99b61679e019666f0570db51ad932=0=0'

def web_scraper(url):

response = requests.get(url)
html = response.content
soup = BeautifulSoup(html, 'lxml')

stock1 = soup.findAll('script')[4].string
stock2 = stock1.split()
stock3 = stock2[3]
# is stock3 sufficient to process as JSON or need further cleaning??

text =  json.dumps(stock3)
print(text)


web_scraper(url)

If it is possible, please give me some pointers. Thank you

Regards,
Henry
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Re: [Tutor] Simultaneous read and write on file

[eryk sun]

On Mon, Jan 18, 2016 at 10:04 PM, Martin A. Brown  wrote:
> The above is a very handy chart.  Did you find this somewhere, eryk
> sun, or is this from your own knowledge and experience?

The mapping to POSIX open flags is from a table in the POSIX fopen
spec [1] as well as the Windows CRT docs for fopen (see the equivalent
oflag table) [2]. The flags for "x" mode can be verified in the Python
3 source [3]. The "x" mode flags are also mentioned in GNU's libc docs
for fopen [4] and open-time flags [5].

The mapping from POSIX open flags to Windows create disposition and
access modes is from the CRT source for the _open function. I can't
provide a source link, but the source code is distributed with MSVC.
For VS2015 it's in lowio/open.cpp, decode_access_flags() and
decode_open_create_flags().

[1]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/fopen.html
[2]: https://msdn.microsoft.com/en-us/library/yeby3zcb
[3]: https://hg.python.org/cpython/file/v3.5.1/Modules/_io/fileio.c#l302
[4]: https://www.gnu.org/software/libc/manual/html_node/Opening-Streams.html
[5]: https://www.gnu.org/software/libc/manual/html_node/Open_002dtime-Flags.html
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Re: [Tutor] Simultaneous read and write on file

[Peter Otten]

Anshu Kumar wrote:

> Hello Everyone,
> 
> I try below code in python 2.7.10 to first create and write into a file
> and
> then read and write that file but what i get is just a  file with new
> content.
> 
> 
 with open('test.txt', 'wb+') as f:
> ... f.write('this is test file.')
> ... f.write('ok!!!')
> ...
 with open('test.txt', 'wb+') as f:
> ... a_str = f.read() + 'read the file'
> ... f.seek(0)
> ... f.write(a_str)
> ...
> 
> 
> I have read in documentation that wb+ mode is for writing and reading. Am
> i using wrong mode, should i use rb+ ?

Quoting https://docs.python.org/2.7/library/functions.html#open

"""
note that 'w+' truncates the file.
"""

That's why you lose the file's current content, and, yes, "r+b" would avoid 
that.

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Re: [Tutor] Simultaneous read and write on file

[Alan Gauld]

On 18/01/16 20:43, Cameron Simpson wrote:

>> The + modes are deceptively appealing but they are full of dangers
>> for precisely the reasons you have discovered(*). You very rarely
>> need them and you are better opening/closing the file and
>> using explicit modes to read/write.
> 
> But if he wants to mix the modes, he certainly should be experimenting. 
> Having 
> a file open for read and write is sometimes useful; I do it myself in certain 
> circumstances.

Yes and so have I. Maybe twice in 30 years of programming.
It's sometimes necessary but it's much, much harder to get
right and very easy to get wrong, usually with data corruption
as a result.

So for a beginner I would never encourage it. For an
experienced programmer sure' if there is no other option
(and especially if you have fixed size records where
things get easier).

> Tip for new players: if you do any .write()s, remember to do a .flush() 
> before 
> doing a seek or a read

That's exactly my point. There are so many things you have
to do extra when working in mixed mode. Too easy to treat
things like normal mode files and get it wrong. Experts
can do it and make it work, but mostly it's just not needed.

> Disagree. As far as his question goes, "wb+" is a correct mode for what he is 
> trying. Whether it is a sensible approach depends very much on what he is 
> doing 
> with his files.

I'm not sure we know what he(?) is trying.
We only know he successfully overwrote his data and
that apparently was not his intention. There are use
cases where it makes sense but in most cases you can
get by just fine without.

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos


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Re: [Tutor] pandas data frame

[Peter Otten]

Bachir Bachir via Tutor wrote:

> Hi Peter Thank you much for your help its very appreciated ,bellow is an
> example of what i need.   The main dataframe ( need to be separated into
> separate dataframes  ). The desired dataframes output correctly as i need
> it to be,Thanks much Main dataframendx V_idAverageMean
>   Peak 0 1  3  2  51  
>   2  2  1  62 3   
>   4 1  83 1  2
>  2  74 2  3 3 
> 65 3  5 3  46 
>1  1 1  87 2   
>   2 5  108 3  5   
>  5  99 1  2 5 
> 10102 5 5  911   
> 3 4 3  10 Dataframe-1ndx V_id 
>  Average MeanPeak 0 1   3  2 
> 53 1   2  2  76 1   1 
> 1  89 1   2  5  10
> Dataframe-2ndx V_idAveragMean Peak 1  2  
> 2  1  64  2   3  3
>  67  2   2  5  10102  
> 5  5  9 Dataframe-3ndx V_idAverageMean   
> Peak 2 3   4  1  85 3 
>  5  3  48 3   5  5
>  9113   4  3  10 Bachir

I see that you got an answer over at comp.python.pydata where you managed to 
get the format a bit more readable ;)

I recommend that you go with Goyo's answer, but instead of the hacky use of
locals() 
 
> >>> locals().update((('dataframe_{}'.format(k), grouper.get_group(k))
> ...  for k in grouper.groups))

I recommend that you put the groups into a normal dict

groups = {k: g.get_group(k) for k in g.groups}

and then access the partial data frames with

v_id = 2
groups[v_id]

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Re: [Tutor] Simultaneous read and write on file

[Cameron Simpson]

On 18Jan2016 16:29, ALAN GAULD  wrote:

On 18/01/16 16:01, Anshu Kumar wrote:

I try below code in python 2.7.10 to first create and write into a file and
then read and write that file but what i get is just a  file with new
content.



with open('test.txt', 'wb+') as f:

... f.write('this is test file.')
... f.write('ok!!!')
...

with open('test.txt', 'wb+') as f:

... a_str = f.read() + 'read the file'
... f.seek(0)
... f.write(a_str)
...


You called f.seek(0) which puts the cursor right back to the start
of the file. Try writing without using the f.seek().


Agreed.


But since you only want to append, it would be better and safer to use
append mode instead.

The + modes are deceptively appealing but they are full of dangers
for precisely the reasons you have discovered(*). You very rarely
need them and you are better opening/closing the file and
using explicit modes to read/write.


But if he wants to mix the modes, he certainly should be experimenting. Having 
a file open for read and write is sometimes useful; I do it myself in certain 
circumstances.


Tip for new players: if you do any .write()s, remember to do a .flush() before 
doing a seek or a read - unlike the C stdio library where the flush is 
automatic in Python the io classes require you to flush written data if you 
read or seek. (You don't have to flush before close, close does that for you.)



(*)Another problem, apart from the risks of overwriting your
data,  is that the + modes will lock the file even while you
are just reading it, which might cause a problem with shared
files)


Only on Windows. On UNIX everything is fine unless you go out of your way to 
make things harder with locking.



I have read in documentation that wb+ mode is for writing and reading. Am i
using wrong mode, should i use rb+ ?


No, you should probably be separately using 'r' to read and 'a'
to append.


Disagree. As far as his question goes, "wb+" is a correct mode for what he is 
trying. Whether it is a sensible approach depends very much on what he is doing 
with his files.


He _may_ be safer opening the file twice - once for "rb" and once for "ab" - 
because he does not have to juggle the modes, but it isn't necessarily what he 
wants.


Cheers,
Cameron Simpson 
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Re: [Tutor] Simultaneous read and write on file

[eryk sun]

On Mon, Jan 18, 2016 at 10:01 AM, Anshu Kumar  wrote:
> I have read in documentation that wb+ mode is for writing and reading. Am i
> using wrong mode, should i use rb+ ?

Use w+ to create a new file, opened with read and write access. Use r+
to open an existing file with read and write access. Unlike w+, r+
does not truncate the file and will not create a new file.

To clarify what Alan said, the "+" modes do not 'lock' the file. On
Windows you may experience a sharing violation if another program
doesn't share write access. This isn't quite the same as a file lock.
All open references to a file have to agree on read, write, and delete
sharing. For example, when Notepad saves a file, it tries to open a
handle that shares only read access. If this open succeeds, Notepad
knows that it's the only writer. (It doesn't care if there are
multiple readers.) On the other hand, if some other program has the
file open with write or delete access, Notepad's open will fail with a
sharing violation. Then it displays a message box saying it can't save
the file because another process has it open, and it offers to save
the file using a different name.

FYI, in terms of POSIX open flags [1], the file mode gets mapped as follows:

  |   flags   |   no +   |   +
-
r |   | O_RDONLY | O_RDWR
w | O_CREAT, O_TRUNC  | O_WRONLY | O_RDWR
a | O_CREAT, O_APPEND | O_WRONLY | O_RDWR

Python 3 only:

x | O_CREAT, O_EXCL   | O_WRONLY | O_RDWR

In terms of Windows open dispositions and access modes [2], the file
mode gets mapped as follows:

  |  disposition  |  no + |+
---
r | OPEN_EXISTING | GENERIC_READ  | GENERIC_READ, GENERIC_WRITE
w | CREATE_ALWAYS | GENERIC_WRITE | GENERIC_READ, GENERIC_WRITE
a | OPEN_ALWAYS   | GENERIC_WRITE | GENERIC_READ, GENERIC_WRITE

Python 3 only:

x | CREATE_NEW| GENERIC_WRITE | GENERIC_READ, GENERIC_WRITE

O_APPEND entails an implicit seek to the end of a file before every
write. Note that Python uses the Windows CRT for file access, which
doesn't use the native FILE_APPEND_DATA access to implement O_APPEND.
Instead it opens the file for generic writing and manually updates the
file pointer. This may cause problems if the security descriptor only
allows appending to a file. In this case you'd have to call CreateFile
directly (e.g. via ctypes or win32api).

[1]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html
[2]: https://msdn.microsoft.com/en-us/library/aa363858
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