Re: [Tutor] How do I recursively remove the contents of a directory??

[w chun]

On 10/20/05, Suri Chitti <[EMAIL PROTECTED]> wrote:
>
> If I have a directory /u01/qa/logs and the logs has a number of children
> directories and I want to remove everything in logs and logs itself, is
> there a single method or command to do that?  I want to avoid recursively
> removing the files in each child directory and so on.


i'd try /bin/rm -rf /u01/qa/logs from the shell.  if you have to do it
programmatically, you can use os.system() with that cmd.

hope this helps!
-- wesley
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
"Core Python Programming", Prentice Hall, (c)2006,2001
http://corepython.com

wesley.j.chun :: wescpy-at-gmail.com
cyberweb.consulting : silicon valley, ca
http://cyberwebconsulting.com
___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] Help(!) with OOP/Composition from "Learning Python"

[Liam Clarke]

On 10/21/05, Andrew P <[EMAIL PROTECTED]> wrote:
> I've been reading about composition vs inheritance, and went back to
> "Learning Python" to look at something I found very confusing a year
> ago.  Turns out I still find it very confusing :)
>
> The code at the bottom was taken from the OOP chapter, it's a solution
> to one of the end-of-chapter problems.
>
> Honestly, this toy program is enough to make my head spin.  Am I too
> stupid for OOP?  Here is me trying to decipher it:
>
>  Starting here:
>
> x = Lunch(  )   # Self-test code
> x.order('burritos') # If run, not imported
>
> You have to look at the method of class Lunch:
>
> def order(self, foodName):  # Start a Customer order simulation.
> self.cust.placeOrder(foodName, self.empl)
>
> check the instance name:
>
> self.cust = Customer(  )
>
> to see what class it belongs to, jump to class Customer, look up the
> method being called:
>
>  def placeOrder(self, foodName, employee):  # Place order with Employee.
> self.food = employee.takeOrder(foodName)
>
>  which uses employee as an argument, which was, looking back up, an
> instance of class Employee:
>
> class Employee:
> def takeOrder(self, foodName):# Return a Food, with requested name.
> return Food(foodName)
>
> which seems to return an instance of food?  I don't really understand
> that,  but I've already forgotten what it was I started off looking to
> find :)
>
> x.result(  )
>
> Which is just entirely too much for my brain to hold at once.  I'm
> sorry if this sounds like whining, but this entire program seems as
> bad as trying to decipher the GOTO-crazy scribblings of a lunatic.
> There is no linearity, and the extra abstraction of the classes just
> adds another layer of complexity.  Instead of functions and arguments
> there are methods, classes, and instances being passed about
> willy-nilly and no (for me) easy way to follow the path or make sense
> of it.
>
> Is this just an example of a technique with a constant complexity
> factor that looks ridiculous on a toy program, but very quickly
> becomes useful on larger ones?  Are there tools that make reading
> something like this more clear?
>
> Thanks,
>
> Andrew
>
>
> #
> # lunch program
> #
>
> class Lunch:
> def __init__(self):# Make/embed Customer and Employee.
> self.cust = Customer(  )
> self.empl = Employee(  )
> def order(self, foodName):  # Start a Customer order simulation.
> self.cust.placeOrder(foodName, self.empl)
> def result(self):   # Ask the Customer about its Food.
> self.cust.printFood(  )
>
> class Customer:
> def __init__(self): # Initialize my food to None.
> self.food = None
> def placeOrder(self, foodName, employee):  # Place order with Employee.
> self.food = employee.takeOrder(foodName)
> def printFood(self):   # Print the name of my food.
> print self.food.name
>
> class Employee:
> def takeOrder(self, foodName):# Return a Food, with requested name.
> return Food(foodName)
>
> class Food:
> def __init__(self, name):  # Store food name.
> self.name = name
>
> if __name__ == '__main__':
> x = Lunch(  )   # Self-test code
> x.order('burritos') # If run, not imported
> x.result(  )
> x.order('pizza')
> x.result(  )
> ___
> Tutor maillist  -  Tutor@python.org
> http://mail.python.org/mailman/listinfo/tutor
>


Hi Andrew,

You've run into one of my biggest peeves when trying to learn OO.
The whole "OO models real world objects" is detrimental when the
examples that are given are pointless to programming. You'll never
model someone ordering pizza. Alan Gauld's tutorial has a decent guide
to OO, but it still takes a bit of getting used to.

That's why I like Python, it doesn't force you into a certain style of
programming, as opposed to something like, say, Java, and it's
somewhat ludicrous Hello World -
http://java.sun.com/docs/books/tutorial/getStarted/application/

The thing is, if you can use a list method or string method, you're
using OO, and when you begin learning, you don't need to know too much
about objects immediately.

I attempted to learn programming via my local university, which taught
Java, and our first lab had us creating the classes Tap (Faucet for
the norteamericanos), Mixer and Basin. While, in retrospect, I can see
that it included some essential bits of Java like multiple
constructors, get/sets, subclassing etc, it was just so pointless, (as
was the rest of the practical stuff until the very last assignment
where one built a calculator) as all you were doing was designing
classes that passed unit tests.

Speaking for myself, I learn best when I come across a problem that
needs a particular solution.

Re: [Tutor] pytunes (Was __slots__, struct, etc.)

[Liam Clarke]

Hmmm, that's interesting.

Obviously, for a playlist with x songs, and n songs by a particular
artist, the optimum separation between songs would be x/n.

Which would be easy for one artist, but for all of them?

Hmm...

Let's see. First off, let's discount all the artists with only one
song, they can be the space filler.

Next, you'd have to work out optimal spacing for each artist's songs,
and try to insert them into a list. If that slot was already taken,
you'd want to look down and up the list for the next free space,
choosing whichever maximised the distance. And you'd have to treat
x[5] - 10 as x[96] for a list x where len(x) == 100.

Err, there's got to be an algorithm for this sorta stuff, but I can't
understand the big words when I google it... what's your solution?

On 10/21/05, John Fouhy <[EMAIL PROTECTED]> wrote:
> Hmm, neat. I don't have any feedback for you on your code, but since
> you're working with this sort of thing, I have a puzzle for you:
>
> Suppose you have a collection of MP3 files.  You want to build a
> random playlist, subject to the condition that tracks by the same
> artist are as far apart as possible.  You can assume you have the
> track / artist data in any structure you like.  How would you do this?
>
> (I have a solution, but I don't think it is optimal.  In fact, I'm not
> sure how to actually define "optimal" here... And so I am interested
> in how other people would solve this problem :-) )
>
> --
> John.
> ___
> Tutor maillist  -  Tutor@python.org
> http://mail.python.org/mailman/listinfo/tutor
>
___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] regular expression matching a dot?

[Christian Meesters]

Hi Frank & Kent & Hugo,

Didn't have the time to read the list yesterday ...

Thanks for pointing me to the regex-debuggers. Though I don't 
considered myself a regex-beginner I had to learn, that now that I'm 
using regexes only occasionally I might need some help here and there.

Cheers,
Christian


Frank Bloeink wrote:
> Hi [Christian|List]
>
> This post is not regarding your special problem (which anyway has been
> solved by now), but I'd like to share some general tip on working with
> regular expressions.
> There are some nice regex-debuggers out there that can help clearify
> what went wrong when a regex doesn't match when it should or vice 
> versa.
>
> Kodos http://kodos.sourceforge.net/ is one of them, but there are many
> others that can make your life easier ; at least in terms of
> regex-debugging ;)
>
> Probably most of you (especially all regex-gurus) know about this
> already, but i thought it was worth the post as a hint for all 
> beginners
>
> hth Frank

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] Dynamic Function Assignment

[Alan Gauld]

for id in ('A', 'B', 'C'):
   if segment.upper().startswith(id):

Think dictionary:

objects = {'A': a, 'B':b, 'C':c}

for id in ('A','B','C')
objects[id].method()

I have a section within my OOP topic that specifically talks about this 
in the context of a collection of bank account objects. You might find 
it worth skimming through.

HTH,

Alan G
Author of the learn to program web tutor
http://www.freenetpages.co.uk/hp/alan.gauld


___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] Time - sum/difference

[Jonas Melian]

I wanted to sum two time values:

-02:30
+01:00
--
-01:30

I found one solution:
 >>> time_local = dt.time(2,30)
 >>> time_str = str(time_local).split(':')

Now I'll can get the first value, convert to integer and sum it.

Kent Johnson wrote:

>Jonas Melian wrote:
>  
>
>>I would get the local time of a country, using UTC (Universal Time 
>>Coordinated) and DST (Daylight SavingTime) of that country.
>>
>>An example, utc time -02:30 and dst +1 :
>>
>>country_utc = datetime.time(2,30)
>>isUTCNegative = True
>>dst = datetime.time(1,0)
>>
>>Now I would the difference of both times.
>>-02:30 + 01:00 -> -01:30
>>
>>Is possible get sum/difference of time values? How?
>>
>>
>
>I'm not exactly sure what you are looking for, but you can subtract 
>datetime.datetime instances. If you are trying to find the difference between 
>local time and utc this is one way:
>
> >>> import datetime as dt
> >>> dt.datetime.now()
>datetime.datetime(2005, 10, 20, 19, 41, 30, 393000)
> >>> dt.datetime.utcnow()
>datetime.datetime(2005, 10, 20, 23, 41, 52, 195000)
> >>> dt.datetime.utcnow()-dt.datetime.now()
>datetime.timedelta(0, 14400)
>
>though there is a race condition here that might give you an error of a 
>millisecond sometimes.
>
>Kent
>
>___
>Tutor maillist  -  Tutor@python.org
>http://mail.python.org/mailman/listinfo/tutor
>
>  
>

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] How do I recursively remove the contents of a directory??

[Alan Gauld]

>If I have a directory /u01/qa/logs and the logs has a number of children
> directories and I want to remove everything in logs and logs itself, is

os.system('rm -rf  %s ' % logpath)

Sometimes its easier to use the OS directly!

If you were selectively deleting files it would be different but for 
the sledgehammer case I'd pobably just go with rm...

Alan g


___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

[Tutor] Fwd: Saving command line keyed input?

[Ed Singleton]

A quick tip for the Windows command line.

Ctrl-C, Ctrl-A etc don't work, neither does right-clicking
(menu-click).  However, right-clicking does work on the blue title
bar.

Right-click on the blue title bar and then go down to Edit and then
you can Select All.  Then right-click on the blue title bar again and
go down to Edit and then Copy.

If at any point you right click in the black part of the window or do
a Ctrl key sequence, it deselects all your text.  Very unintuitive, as
it is completely different to every other Windows app.  (I think they
do it on purpose to stop people wanting to use the Command Line).

Ed

On 19/10/05, CPIM Ronin <[EMAIL PROTECTED]> wrote:
> I know that one should use IDLE or a choosen editor for any substantial
> Python coding! However, if one  happens to have written some interesting
> doodlings on the regular command line interface (under Windows XP in my
> case), is there an easy way to save ALL input to date into a selected file?
>
> For example:
> >>>class work_center:
>  def __init__(self,x_name):
> self.name = x_name
>
> >>>x = work_center("machine press")
> >>>
>
>   ---  What do I do to save the above work into a file named "mywork.py"
>
> Thanks.
>
> RC
>
> _
> On the road to retirement? Check out MSN Life Events for advice on how to
> get there! http://lifeevents.msn.com/category.aspx?cid=Retirement
>
> ___
> Tutor maillist  -  Tutor@python.org
> http://mail.python.org/mailman/listinfo/tutor
>
___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] Help(!) with OOP/Composition from "Learning Python"

[Kent Johnson]

Andrew P wrote:
> I've been reading about composition vs inheritance, and went back to
> "Learning Python" to look at something I found very confusing a year
> ago.  Turns out I still find it very confusing :)
> 
> The code at the bottom was taken from the OOP chapter, it's a solution
> to one of the end-of-chapter problems.
> 
> Honestly, this toy program is enough to make my head spin.  Am I too
> stupid for OOP?  Here is me trying to decipher it:

You did a pretty good job!
> 
> Which is just entirely too much for my brain to hold at once.  I'm
> sorry if this sounds like whining, but this entire program seems as
> bad as trying to decipher the GOTO-crazy scribblings of a lunatic. 
> There is no linearity, and the extra abstraction of the classes just
> adds another layer of complexity.  Instead of functions and arguments
> there are methods, classes, and instances being passed about
> willy-nilly and no (for me) easy way to follow the path or make sense
> of it.

I agree with the other posters that this is not a very good example of OOP. It 
shows some of the nuts and bolts of OOP - objects containing objects, invoking 
methods on objects and dividing responsibility between different classes - but 
it doesn't use them well and the motivation is lacking.

Fundamentally classes are a way to package state (variables) and behaviour 
(functions) into a single abstraction. Done well, the resulting class has a 
coherence and utility of its own.

For simple examples just look at Python's built in string, list and dict 
classes. In each case, the class hides considerable complexity and provides a 
useful abstraction. You can use a list without worrying about the details of 
how the list items are stored, how the storage is allocated, what happens when 
new storage is needed, etc., etc. You have at your disposal a sort() algorithm 
that has been tuned for high performance by top-notch programmers over many 
years, and much more.

You can also think of classes very pragmatically, as another tool available to 
organize your code, just like modules and functions. Classes add some useful 
capabilities to your toolkit. This essay gives some simple motivating examples 
of why a beginner might want to use classes:
http://personalpages.tds.net/~kent37/blog/stories/15.html

> 
> Is this just an example of a technique with a constant complexity
> factor that looks ridiculous on a toy program, but very quickly
> becomes useful on larger ones?  Are there tools that make reading
> something like this more clear?

There is a very real cost to OOP that responsibility for some action can be 
distributed among multiple cooperating classes, so to trace through an 
operation you may have to follow a chain from one class to the next. When the 
design is well done, the benefit of useful abstractions outweighs this cost. 
Done poorly, you can write object-oriented spaghetti code. The key is to have a 
clear idea of the responsibility of each class. 

Stepping through the code in a debugger can be useful to understanding the flow.

Kent

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] How do I recursively remove the contents of a directory??

[Kent Johnson]

Suri Chitti wrote:
> If I have a directory /u01/qa/logs and the logs has a number of children 
> directories and I want to remove everything in logs and logs itself, is 
> there a single method or command to do that?  I want to avoid 
> recursively removing the files in each child directory and so on.

shutil.rmtree() (which actually does recursively remove all the children)

Kent

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] Fwd: Saving command line keyed input?

[Kent Johnson]

Ed Singleton wrote:
> A quick tip for the Windows command line.
> 
> Ctrl-C, Ctrl-A etc don't work, neither does right-clicking
> (menu-click).  However, right-clicking does work on the blue title
> bar.
> 
> Right-click on the blue title bar and then go down to Edit and then
> you can Select All.  Then right-click on the blue title bar again and
> go down to Edit and then Copy.

If you turn on Quick Edit (from Properties in the right-click menu) then you 
can select text and right-click to copy, then right-click again to paste.

Kent

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] greetings...

[Gabriel Farrell]

Welcome to the list, Carl.  Feel free to browse the list archive at
http://mail.python.org/pipermail/tutor/ or
http://aspn.activestate.com/ASPN/Mail/Browse/Threaded/python-Tutor to
get some idea of the kinds of questions asked and answers given.
You'll find a lot of suggestions for beginners among the threads there
as well.

There's also http://wiki.python.org/moin/BeginnersGuide, which is
always a good place to start.

gsf


On Thu, Oct 20, 2005 at 05:09:07PM -0400, [EMAIL PROTECTED] wrote:
> Greetings to list,
> Tomorrow is my last day in class with Lutz. I am not only new to Python but
> new to programming in general, this is my first language. Looking forward to
> your help in the days and weeks to come.
> Any suggestions for self tutorial, whether on python.org
> or not, would be greatly appreciated. I am going to
> finish his Learning...
> book first then hack open some open code for a simple project in order to
> see how it works.
> peace
> Carl

> ___
> Tutor maillist  -  Tutor@python.org
> http://mail.python.org/mailman/listinfo/tutor

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

[Tutor] perldoc - confused!

[Dan Klose]

Hello Python List,

When using perl I tend to use perldoc.

I spent ages today trying to list all items in a directory, simple I now
know (os.listdir) but I was trying to use os.walk simply because I had
no idea that listdir existed.  I only found listdir because I was
reading about walk

Is there a python version of perldoc?

Thanks for any guidance

Dan.

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] Fwd: Saving command line keyed input?

[w chun]

On 10/21/05, Kent Johnson <[EMAIL PROTECTED]> wrote:
> Ed Singleton wrote:
> > A quick tip for the Windows command line.
> >
> > Ctrl-C, Ctrl-A etc don't work, neither does right-clicking
> > (menu-click).  However, right-clicking does work on the blue title
> > bar.
>
> If you turn on Quick Edit (from Properties in the right-click menu) then you 
> can select text and right-click to copy, then right-click again to paste.


so yes, ed and kent are right.  you have to do those things if you're
running Python from the DOS window.   Ctrl-A, Ctrl-C, Ctrl-V work from
the IDLE window and most non-DOS win32 windows..

-- wesley
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
"Core Python Programming", Prentice Hall, (c)2006,2001
http://corepython.com

wesley.j.chun :: wescpy-at-gmail.com
cyberweb.consulting : silicon valley, ca
http://cyberwebconsulting.com
___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

[Tutor] self knowledge

[Ethan Ligon]

I've devised a simple class; one of the class attributes is an identifier.

Thus,

class Foo:
  def __init__(self,name):
self.name=name

When using the class in practice, I've found it natural to
create instances of Foo so that the instance itself is called
name.  Thus, I find myself doing things like:

>>> a=Foo('a')
>>> b=Foo('b')

I want the name attribute to depend only on the name of the
original variable; thus

>>> c=a
>>> c.name
'a'

is the desired behavior. 

But this is plainly silly--I'm supplying information on identity
twice when I instantiate each instance---and gives rise to 
two questions. 

First, my immediate inclination is to try and think of 
a way for the object to know its own name (at the time
its instantiated) without being told, perhaps via the 
creation of a name method for Foo.  But the only ways 
I can think of learning this name are all incredibly 
awkward and kludgy.  What's the best way to do this?

Second, because this seems awkward, I strongly suspect 
that there's a pretty fundamental problem with the way
I'm approaching the problem.  When the name of a variable
is itself information which might be useful, what's the
right way convey this information?  

Thanks,
-Ethan

-- 
Ethan Ligon, Assoc. Professor   [EMAIL PROTECTED]
Dept. of Agricultural & Resource Economics
University of Californiahttp://are.berkeley.edu/~ligon
Berkeley, CA 94720-3310  (510)643-5411
___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

[Tutor] : Threads?

[Orri Ganel]

Hello all,

I've been working on a program for a week or two now that will convert 
all the wav files in a folder to mp3s, filling the id3 tags with the 
correct information as collected from gracenote.com.  This part works 
fine.  However, the actual conversion to mp3 takes between 30 and 50 
seconds per song, so it's usually about 10 minutes per album.  With this 
in mind, I thought, why not try to use threads so all the conversions 
happen simultaneously?  That way, the whole album will take between 30 
and 50 seconds.  Unfortunately, I can't seem to get a working threaded 
version that significantly reduces the time involved . . . The 
unthreaded version is available at 
http://rafb.net/paste/results/Y1DTnW54.html, and the current, only 
slightly time-improved threaded version is available at 
http://rafb.net/paste/results/Lvsjj495.html. Any and all suggestions as 
to how to threadify this are welcome.  I realize the code isn't as 
pretty as it could be, but first I want to make a threaded version that 
works.  Once this has been accomplished, I'll finish commenting the code 
and making it more user-friendly to read.

Thanks in advance,
Orri

P.S. - In order to make my code work, it is necessary to download 
several modules. Once the code works, I'll include above the code a 
comment listing all the requirements. Right now, I believe the following 
modules are needed:

ClientForm - http://wwwsearch.sourceforge.net/ClientForm/
id3writer - 
http://www.comfortableshoe.co.uk/cgi-bin/blosxom.cgi/Home/Python/id3Writer.comments
 
(click the "download link" link)
id3reader - 
http://www.comfortableshoe.co.uk/cgi-bin/blosxom.cgi/Home/Python/id3Writer.comments
 
(click the "Ned Batchelder's id3Reader" link)
PyID3 - http://sourceforge.net/projects/pyid3
threadpool - http://chrisarndt.de/en/software/python/threadpool.html

I also considered using the following, but decided not to for reasons of 
difficulty of use or lack of desired operations:

PyID3Tag - http://superduper.net/?page=pyid3tag
ID3-Py - http://id3-py.sourceforge.net/

The following non-Python program is also needed:

Lame - http://lame.sourceforge.net/download/download.html

-- 
Email: singingxduck AT gmail DOT com
AIM: singingxduck
Programming Python for the fun of it.

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] self knowledge

[Kent Johnson]

Ethan Ligon wrote:
> I've devised a simple class; one of the class attributes is an identifier.
> 
> Thus,
> 
> class Foo:
>   def __init__(self,name):
> self.name=name
> 
> When using the class in practice, I've found it natural to
> create instances of Foo so that the instance itself is called
> name.  Thus, I find myself doing things like:
> 
> 
a=Foo('a')
b=Foo('b')

Why does this matter? Why do you need the name both places?

> First, my immediate inclination is to try and think of 
> a way for the object to know its own name (at the time
> its instantiated) without being told, perhaps via the 
> creation of a name method for Foo.  But the only ways 
> I can think of learning this name are all incredibly 
> awkward and kludgy.  What's the best way to do this?

The only ways to do this are awkward and kludgy - you have to inspect the stack 
and find out the name of the variable in the caller. Don't do it.

> 
> Second, because this seems awkward, I strongly suspect 
> that there's a pretty fundamental problem with the way
> I'm approaching the problem.  When the name of a variable
> is itself information which might be useful, what's the
> right way convey this information?  

I think this is the third time this question has come up this week! Usually the 
answer is to put your data in a dictionary or list. Here is another version:
http://mail.python.org/pipermail/tutor/2005-October/042371.html


___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] : Threads?

[Kent Johnson]

Orri Ganel wrote:
> Hello all,
> 
> I've been working on a program for a week or two now that will convert 
> all the wav files in a folder to mp3s, filling the id3 tags with the 
> correct information as collected from gracenote.com.  This part works 
> fine.  However, the actual conversion to mp3 takes between 30 and 50 
> seconds per song, so it's usually about 10 minutes per album.  With this 
> in mind, I thought, why not try to use threads so all the conversions 
> happen simultaneously?  That way, the whole album will take between 30 
> and 50 seconds.  Unfortunately, I can't seem to get a working threaded 
> version that significantly reduces the time involved . . . The 

The only part you are doing in a thread is the actual conversion. This is 
likely to be CPU-intensive so running it in multiple threads may not help - you 
still have only the one CPU to run on. To the extent that you can overlap disk 
I/O in one conversion with processing in another you may get a win; on the 
other hand you could just as well have contention for the disk as you try to 
read and write a bunch of files at the same time.

The fetch from gracenote.com seems like a better candidate for threading 
because there is some latency...but the total time is still probably small 
compared to the conversion time.

Maybe if you have multiple CPUs you can get a speedup by using as many threads 
as CPUs...I'm not sure how os.system() behaves in this case. You may have to 
explicitly fork to get a new process.

Hmm...come to think of it, os.system() may block other threads, I don't 
know...you could try subprocess.Popen() instead.

Kent

> unthreaded version is available at 
> http://rafb.net/paste/results/Y1DTnW54.html, and the current, only 
> slightly time-improved threaded version is available at 
> http://rafb.net/paste/results/Lvsjj495.html. Any and all suggestions as 
> to how to threadify this are welcome.  I realize the code isn't as 
> pretty as it could be, but first I want to make a threaded version that 
> works.  Once this has been accomplished, I'll finish commenting the code 
> and making it more user-friendly to read.
> 
> Thanks in advance,
> Orri
> 
> P.S. - In order to make my code work, it is necessary to download 
> several modules. Once the code works, I'll include above the code a 
> comment listing all the requirements. Right now, I believe the following 
> modules are needed:
> 
> ClientForm - http://wwwsearch.sourceforge.net/ClientForm/
> id3writer - 
> http://www.comfortableshoe.co.uk/cgi-bin/blosxom.cgi/Home/Python/id3Writer.comments
>  
> (click the "download link" link)
> id3reader - 
> http://www.comfortableshoe.co.uk/cgi-bin/blosxom.cgi/Home/Python/id3Writer.comments
>  
> (click the "Ned Batchelder's id3Reader" link)
> PyID3 - http://sourceforge.net/projects/pyid3
> threadpool - http://chrisarndt.de/en/software/python/threadpool.html
> 
> I also considered using the following, but decided not to for reasons of 
> difficulty of use or lack of desired operations:
> 
> PyID3Tag - http://superduper.net/?page=pyid3tag
> ID3-Py - http://id3-py.sourceforge.net/
> 
> The following non-Python program is also needed:
> 
> Lame - http://lame.sourceforge.net/download/download.html
> 

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] : Threads?

[Orri Ganel]

Kent Johnson wrote:

>Orri Ganel wrote:
>  
>
>>Hello all,
>>
>>I've been working on a program for a week or two now that will convert 
>>all the wav files in a folder to mp3s, filling the id3 tags with the 
>>correct information as collected from gracenote.com.  This part works 
>>fine.  However, the actual conversion to mp3 takes between 30 and 50 
>>seconds per song, so it's usually about 10 minutes per album.  With this 
>>in mind, I thought, why not try to use threads so all the conversions 
>>happen simultaneously?  That way, the whole album will take between 30 
>>and 50 seconds.  Unfortunately, I can't seem to get a working threaded 
>>version that significantly reduces the time involved . . . The 
>>
>>
>
>The only part you are doing in a thread is the actual conversion. This is 
>likely to be CPU-intensive so running it in multiple threads may not help - 
>you still have only the one CPU to run on. To the extent that you can overlap 
>disk I/O in one conversion with processing in another you may get a win; on 
>the other hand you could just as well have contention for the disk as you try 
>to read and write a bunch of files at the same time.
>
>The fetch from gracenote.com seems like a better candidate for threading 
>because there is some latency...but the total time is still probably small 
>compared to the conversion time.
>
>Maybe if you have multiple CPUs you can get a speedup by using as many threads 
>as CPUs...I'm not sure how os.system() behaves in this case. You may have to 
>explicitly fork to get a new process.
>
>Hmm...come to think of it, os.system() may block other threads, I don't 
>know...you could try subprocess.Popen() instead.
>
>Kent
>
Thanks for the tip.  Unfortunately, I only have 1 CPU and not the 
slightest idea how to code for multiple CPUs in any case.  Looks like 
I'll just hafta deal with a 10-minute time per album.

-- 
Email: singingxduck AT gmail DOT com
AIM: singingxduck
Programming Python for the fun of it.

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] Help(!) with OOP/Composition from "Learning Python"

[Andrew P]

On 10/21/05, Kent Johnson <[EMAIL PROTECTED]> wrote:

>For simple examples just look at Python's built in string, list and dict
>classes.

-Using- OOP isn't the problem :)  It's impossible to ignore it's usefulness when
programming in Python.  But getting from there to thinking non-procedurally is,
as has been pointed out, a tiny bit difficult.

My frustration/abject fear was with this particular example being very hard to
decipher, and not seeing any advantages to it being laid out that way.  I
assumed there were some, where this kind of thing had benefits.

>You can also think of classes very pragmatically, as another tool available to
>organize your code, just like modules and functions. Classes add some useful
>capabilities to your toolkit. This essay gives some simple motivating examples
>of why a beginner might want to use classes:
>http://personalpages.tds.net/~kent37/blog/stories/15.html


I realize after all these reposnses that I should have mentioned that  I do use
classes to do exactly that.  Bundle logic and data, but then call the classes
I've made procedurally.  It's handy, having methods attached to objects, and to
be able to use any object that supports the same interface interchangeably.

But I have the nagging feeling I still have it all upside down and inside out.
Writing a bunch of objects that are supposed to interact in dynamic ways at
runtime with nobody leading the band, and all.  Maybe if I'm not writing a
a library or framework I shouldn't worry so much.

>
>There is a very real cost to OOP that responsibility for some action can be
>distributed among multiple cooperating classes, so to trace through an
>operation you may have to follow a chain from one class to the next. When the
>design is well done, the benefit of useful abstractions outweighs this cost.
>Done poorly, you can write object-oriented spaghetti code. The key is to have a
>clear idea of the responsibility of each class.
>

For all I know people are using IDEs that let them write unreadable code that
simultaneously allows loosest coupling between classes, and most reuse of code
at the expense of readability.  Giant jellyfish-like automatons that are easy
to maintain with appropriate tools.  I'm still not sure that impression is
wrong :)

I do my best learning by reading good examples.  I imagine most people do.
There is just no substitute for understanding what somebody else has done well,
tip to tail.  I am just mistrustful of something so hard to puzzle out.

>Stepping through the code in a debugger can be useful to
understanding the flow.

I've never actually used a Python debugger. Or any debugger.  That was such a
commonsense answer I'm embarassed I didn't try it first.

Thanks again, Kent :)
___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] Help(!) with OOP/Composition from "Learning Python"

[Kent Johnson]

Andrew P wrote:
> On 10/21/05, Kent Johnson <[EMAIL PROTECTED]> wrote:
>>You can also think of classes very pragmatically, as another tool available to
>>organize your code, just like modules and functions.
> 
> I realize after all these reposnses that I should have mentioned that  I do 
> use
> classes to do exactly that.  
> 
> But I have the nagging feeling I still have it all upside down and inside out.
> Writing a bunch of objects that are supposed to interact in dynamic ways at
> runtime with nobody leading the band, and all.  Maybe if I'm not writing a
> a library or framework I shouldn't worry so much.

Hmm...there are probably some programs like that...maybe a large framework like 
Twisted. Most of my use of classes is fairly prosaic, just a way to organize 
code so it makes sense. Class instances are usually related by simple 
containment in a loose hierarchy of some sort.

> For all I know people are using IDEs that let them write unreadable code that
> simultaneously allows loosest coupling between classes, and most reuse of code
> at the expense of readability.  Giant jellyfish-like automatons that are easy
> to maintain with appropriate tools.  I'm still not sure that impression is
> wrong :)

Well, except for the "easy to maintain with appropriate tools" you are probably 
right. In fact I have the misfortune of working on a system like that right 
now. Without appropriate tools, whatever they may be.
> 
> I do my best learning by reading good examples.  I imagine most people do.
> There is just no substitute for understanding what somebody else has done 
> well,
> tip to tail.  I am just mistrustful of something so hard to puzzle out.

This thread has a few suggestions:
http://groups.google.com/group/comp.lang.python/browse_frm/thread/da095d94c77fe2c7?q=code+examples&hl=en&;

Kent

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] perldoc - confused!

[Danny Yoo]

> I spent ages today trying to list all items in a directory, simple I now
> know (os.listdir) but I was trying to use os.walk simply because I had
> no idea that listdir existed.  I only found listdir because I was
> reading about walk

You should have a 'pydoc' utility.  It's also possible to get help from
the interactive prompt by doing 'help()'.

Good luck!

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] Can anyone teach me...?

[Jacob S.]

>>>I use Delphi for most of my real-world heavy duty GUI work.
>>>
>> Have you tried Boa Constructor? It is quite similar to Delphi. It builds
>> wxPython.
>
> I tried it a couple of years ago but couldn't get it to work!
>
> Even if I had it didn't offer many of the features of VB/Delphi such
> as live database table views and close integration with the underlying
> objects, it simply built a GUI with hooks for the event handlers.
> A big step up from manually assembling TKInter in terms of simplicity
> but the gain wasn't that much in real speed terms.
>
> It would be interesting to see how BOa and Glade have come on
> the last couple of years
>
> Alan G.

I didn't like PythonCard when I tried it, because I couldn't get it to merge
the rcpy(?) file into the main py file and then there was all of the import
the module into its own namespace, etc.  It didn't go over well with me.

Next, I checked out VB, great for building GUIs, but I have to agree that
the code isn't that great after a year of python. I, too, found myself
trying to find things in the library that weren't there. However, I was
prepared to get to know VB well.  I liked the ease of GUI building and the
ability to make a stand-alone exe that the Professional Edition offered.

Then, I did a little research on Boa-Constructor. I have heard on the list
that it is a little unstable.  The reason for this is the storing of the
placement inside the main code blocks. As mentioned above, PythonCard uses a
rcpy file to store these values, so it doesn't need to specially parse the
main code block.  However, I found that if I followed the style of the
generated code, I could edit it directly. Otherwise, the parser runs into an
error when you try to start the designer again. That's why there is the
commented notice at the top of the _init_ctrls_ (or whatever it is) function
that says #Generated method - do not edit   Also, I noticed that the
__init__ block was not affected by control placement, and therefore not
parsed when the frame designer is started.  This is good. All of my class
level changes occur in the __init__ block, any initial lists are sent to
listboxes there, etc.  If you wish to delete an event, you might or might
not have to change some of the generated code depending on whether you do it
properly or not.  If you delete the code directly, the parser doesn't catch
the ids that it generated for the now-non-existent events.  I also like the
ability of it to use the very versatile wxPython library.  Strangely,
though, it doesn't seem to incorporate all of the wx library. Does anybody
know why this is/when they will fix that? (Or how to fix it now?)  I found
it relatively easy to merge the separate files into one file after I
finished the applications I did, and it has a very similar interface to that
of VB. With a little more work, it could be the all powerful VB GUI
building, python coding mix that was mentioned before. Ask for code and I
will send! (maniacal laughter)

Oh, and if you need help learning, I'm here
[EMAIL PROTECTED]
and I'm sure that the members on the list will be as forgiving with you as 
they are with several others who ask questions that they could find on their 
own with enough searching. (I know some will disagree with me, that's why I 
provided my email address specifically if it becomes a problem.)

Jacob ;-)

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] code improvement for beginner ?

[Jacob S.]

> Text mode is the default, you have to specify the 'b' if you want binary 
> mode. And open() seems to accept any mode quite happily:
>
> >>> f=open('build.xml', 'rt')
> >>> f
> 
> >>> f.close()
> >>> f=open('build.xml', 'rabcd')
> >>> f
> 
>
> Kent

I'll bet you'll find that open() is coded something like the following

def open(filename,mode="r"):
if mode = 'w':
dosomething()
if mode = 'wb':
dosomething()
if mode = 'w+':
dosomething()
if mode = 'rb':
dosomething()
...
else:
dosomething()  # Where this assumes you are using default mode "r"

This flow control with emphasis on the else means that if the mode doesn't 
match anything other than "r", then return file object mode "r"

Let's see, now that I'm checking whether that's true, it doesn't quite match 
up. A file that's opened with "r" will check to see whether the file exists 
or not, whereas a file opened with nonsense does not. Ahh. That's because 
you can write to a file opened with nonsense. So instead the function (if it 
were written in python and not C) would probably look like this instead.

def open(filename, mode="r")
if mode = "r":
dosomethingread()
if mode = "rb":
dosomethingreadbin()
if mode = "w+":
dosomethingwriteupd()
...
else:
dosomethingwrite()   # Where write is in the else clause, but 
read is the default value for mode

Phew.

This seems strange. Why don't they put write in the control flow above with 
a raise statement in the else clause?

HTH,
Jacob

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] self knowledge

[Alan Gauld]

Hi Ethan,

> When using the class in practice, I've found it natural to
> create instances of Foo so that the instance itself is called
> name.  Thus, I find myself doing things like:
>
 a=Foo('a')
 b=Foo('b')
>

This is very common at the interactive prompt.
However its nearly always the wrong thing to do in a real world
type program. For one thing how will the code elsewhere in your
programme know about these new object names? You would
need to find a way for every point in your code to gain awareness
of all the names currently in use! In fact Python does provide
ways of doing that because the mnames are hekld in system
dictionaries which you can access but its extre,mekly kludgy!

Much better is to create your instances in a dictionary with the
key being the name. Thus in your example:

>>> objects = {} # empty dictionary
>>> objects['a']=Foo('a')
>>> objects['b']=Foo('b')

You then access the objects with

objects[name].method()

slightly more typing but much easier to use because you can
iterate over all the objects in the dictionary with

for obj in objects:
   obj.dosomething()

Otherwise you would need to know all the object names
and call each in turn or resort to "black magic" to access
the Python internal dictionaries.

> I want the name attribute to depend only on the name of the
> original variable

Now that's a different proposition.
Do you want the name to depend on the prebviously created
variable or the variable name to depend on the object attribute?

If you want the object attribute to depend on the variable name
thats very strange. What happens when you pass the object to
amother namespace? Or if you save to a file or database and
then restore, will it always be associated with the same variable?

Can you explain why you believe that would be useful?

 c=a
 c.name
> 'a'
>
> is the desired behavior.

OK, Thats different again.

That could be done as shoewn above with

>>> c = objects['a']
>>> c.name

> First, my immediate inclination is to try and think of
> a way for the object to know its own name (at the time
> its instantiated) without being told

variables in python are merely references to an object, the object is not 
actually called by the name of the variable. Consider:

a = C() # an instance of c
b = a# both a and b point at the instance

which is the name of the C instance? Is it a or b or neither?

>>> id(a)
>>> id(b)

shows that the objects real identity is a number which is
unrelated to either 'a' or 'b'

> Second, because this seems awkward, I strongly suspect
> that there's a pretty fundamental problem with the way
> I'm approaching the problem.  When the name of a variable
> is itself information which might be useful, what's the
> right way convey this information?

Yes you are trying tonsolve the wrong problem.
Instances created dynamically at runtime are best kept in
a container (list or dictionary) and managed as a group or
selected on demand. A dictionary is usually the best option.

After all thats why Python uses dictionaries under the hood
for its own purposes!

FWIW I give an example of this problem in the OOP topic
of my tutor, in the bank account example where we need to
store a collection of bank accounts by account ID.

HTH,

Alan G
Author of the learn to program web tutor
http://www.freenetpages.co.uk/hp/alan.gauld


___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] : Threads?

[Alan Gauld]

> in mind, I thought, why not try to use threads so all the conversions 
> happen simultaneously?  That way, the whole album will take between 30 
> and 50 seconds.  

One possible problem with this is that the activity is disk IO bound.
In fact using too many threads could even slow the thing down as 
the HD head spends all its time shunting between files.

If you keep the thread count down to two or three you might get 
a noticable improvement but one thread per track, unless you have 
a lot of separate hard disk spindles to distribute the work will 
not help much I suspect.


Alan G.
___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] code improvement for beginner ?

[Kent Johnson]

Jacob S. wrote:
>> Text mode is the default, you have to specify the 'b' if you want 
>> binary mode. And open() seems to accept any mode quite happily:
>>
>> >>> f=open('build.xml', 'rt')
>> >>> f
>> 
>> >>> f.close()
>> >>> f=open('build.xml', 'rabcd')
>> >>> f
>> 
>>
>> Kent
> 
> 
> I'll bet you'll find that open() is coded something like the following
> 
> def open(filename,mode="r"):
>if mode = 'w':
>dosomething()
>if mode = 'wb':
>dosomething()
>if mode = 'w+':
>dosomething()
>if mode = 'rb':
>dosomething()
>...
>else:
>dosomething()  # Where this assumes you are using default mode "r"

One of the cool features of Python is that you can look at the source code to 
answer questions like this.

open() is implemented in Objects/fileobject.c. Not too surprisingly, it 
delegates to the underlying C implementation for the actual open call. On 
Windows it converts the name and mode to Unicode and calls _wfopen(); on other 
platforms it calls fopen().

The ANSI C standard says,
The argument mode points to a string. If the string is one of the following, 
the file is
open in the indicated mode. Otherwise, the behavior is undefined.

If the string begins with one of the [below] sequences, the implementation 
might choose to ignore the remaining characters, or it might use them to select 
different kinds of a file (some of which might not conform to the properties in 
7.19.2).

r open text file for reading
w truncate to zero length or create text file for writing
a append; open or create text file for writing at end-of-file
etc

so it seems the implementation is free to ignore characters it doesn't 
understand after a valid initial sequence.

Kent

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] is mxDateTime recommended?

[Lance E Sloan]

--On Thursday, October 20, 2005 4:44 PM -0400 Kent Johnson <[EMAIL PROTECTED]> 
wrote:
> Since 2.3 Python includes a datetime module which has some facility for
> date calculations. I think mxDateTime is more sophisticated but if your
> needs are simple take a look at datetime.

I think I would like to use the "datetime" module included with Python, 
just so I don't need to worry about an additional piece of code, the 
"mxDateTime" module.

In my code, I set up some mxDateTime RelativeDateTime objects that will be 
used later:

  secondLockBeginsDelta = DateTime.RelativeDateTime( day = 14, hour = 23,
  minute = 59, months = -4 )

When I add that to another mxDateTime object, the month, hour, and minute 
get set to those absolute values, but the month is reduced by four.  I know 
I won't be able to exactly the same thing with datetime.  I think I could 
do something like this (semi-pseudocode):

  firstTime = datetime.now()
  secondTime = firstTime - timedeltaFourMonthsObject
  secondTime.replace( day = 14, hour = 23, minute = 59 )

The problem is that I can't figure out how to create that 
timedeltaFourMonthsObject.  The datetime timedelta class constructor 
doesn't allow creating a delta with a month.  Any suggestions?

(I think it's a little too bad that the timedelta class represents all 
deltas as days and seconds.  That must be why they don't support months, 
since months have different lengths.  IMHO...)

Also, how can I make a copy of a datetime object?

  timeA = datetime.now()
  timeB = timeA # copy or reference to same object?

--
Lance E Sloan, Systems Research Programmer III
U-M WATS: Web Applications, Technologies, and Solutions
Full-service web and database design, development, and hosting.
http://www.itcs.umich.edu/wats/ - "Putting U on the Web"

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] is mxDateTime recommended?

[Kent Johnson]

Lance E Sloan wrote:
> When I add that to another mxDateTime object, the month, hour, and 
> minute get set to those absolute values, but the month is reduced by 
> four.  I know I won't be able to exactly the same thing with datetime.  
> I think I could do something like this (semi-pseudocode):
> 
>  firstTime = datetime.now()
>  secondTime = firstTime - timedeltaFourMonthsObject
>  secondTime.replace( day = 14, hour = 23, minute = 59 )
> 
> The problem is that I can't figure out how to create that 
> timedeltaFourMonthsObject.  The datetime timedelta class constructor 
> doesn't allow creating a delta with a month.  Any suggestions?
> 
> (I think it's a little too bad that the timedelta class represents all 
> deltas as days and seconds.  That must be why they don't support months, 
> since months have different lengths.  IMHO...)

This thread may help:
http://groups.google.com/group/comp.lang.python/browse_frm/thread/6c751e2845932c20/08466fb5a150dd9e?hl=en#08466fb5a150dd9e


> Also, how can I make a copy of a datetime object?
> 
>  timeA = datetime.now()
>  timeB = timeA # copy or reference to same object?

Reference to the same object.

one way is:
import copy
timeB = copy.copy(timeA)

Kent

___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] is mxDateTime recommended?

[Tim Peters]

[Lance E Sloan]
> ...
> (I think it's a little too bad that the timedelta class represents all
> deltas as days and seconds.

And microseconds.

> That must be why they don't support months, since months have
> different lengths.  IMHO...)

That's right.  It's hard to argue about what days, seconds and
microseconds mean (note that I didn't say it's impossible <0.5 wink>).
 Exactly what "a month" means depends on who you ask, when you ask it,
and what they're doing at the time.  That is, there is no answer to
the question that doesn't assume some policy that, while it may help
some people some of the time, would at least as often get in the way
for other people.  datetime tries to be like, say, integers that way: 
a solid base with clear semantics, but if you want square roots you're
gonna have to define what the heck you mean by that and do it yourself
;-)

> Also, how can I make a copy of a datetime object?

It's almost certainly the case that you don't really want to, but are
suffering a confusion about something else that makes you _think_ you
want to.  It's hard to guess what that may be unless you can explain
clearly what you think "making a copy" would _accomplish_ for you.  It
will almost certainly turn out to be the case that it would not
accomplish what you're really after, or that there's no advantage in
accomplishing it.  datetime objects are (again like integers)
immutable:  there is nothing anyone can do to _change_ the value of a
datetime object.  In a nutshell, that's why "making a copy" is almost
certainly irrelevant.  For example, if you see that d.month is 7 at
some point, d.month will always be 7 thereafter, no matter what other
code you may run, just so long as `d` is bound to the same datetime
object for the duration.  There are no operations in the language that
can mutate a datetime object's value.

>  timeA = datetime.now()
>  timeB = timeA # copy or reference to same object?

Same object, and it makes no difference to that answer in Python no
matter what appears on the right side of the first statement.  You
happened to use a datetime.date in this example, but it would be the
same answer if you used an integer, string, list, tuple, function,
bound method object, class, array, module, file ..., any object
whatsoever.  No exceptions.

[Kent Johnson]
> import copy
> timeB = copy.copy(timeA)

That does happen to make a distinct physical copy today, but there's
no guarantee it will always do so.  In general, _any_ operation is
free to return a pre-existing instance of an object of an immutable
type, if it has the correct value.  Again there are no exceptions to
that rule.  Here's an example where copy.copy() doesn't happen to make
a distinct physical copy today:

>>> import copy
>>> two = 2
>>> another_2 = copy.copy(2)
>>> two is another_2
True

Again, if anyone thinks "bad consequences" may follow from this, it's
almost certainly the case that they misunderstand something else about
Python.  There is simply no way to tell whether two immutable objects
with the same _value_ are or aren't the same physical object without
looking at their memory addresses, and it's extremely rare for sane
 Python code to give a hoot about exactly where an object
happens to reside in RAM.
___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor

Re: [Tutor] : Threads?

[Orri Ganel]

I'll try doing 3 or 4 tracks per thread, then. Thanks for the advice.If you keep the thread count down to two or three you might get
a noticable improvement but one thread per track, unless you havea lot of separate hard disk spindles to distribute the work willnot help much I suspect.Alan G.
-- Email: singingxduck AT gmail DOT comAIM: singingxduckProgramming Python for the fun of it.
___
Tutor maillist  -  Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor