About reading Python code

**WaterWalk** · Mar 17 '08, 04:05 AM

Re: About reading Python code

On Mar 17, 11:54 am, WaterWalk <toolmas...@163 .comwrote:

Hello. I wonder what's the effective way of figuring out how a piece
of python code works. With C I often find it very useful to be able to
run the code in step mode and set breakpoints in a debugger so I can
watch how the it executes, how the data change and how the code jumps
from one function to another. But with Python, the debugger is a
little primitive. The default IDLE doesn't even allow me to set a
breakpoint. When the code is long, I am often lost in it.
>
So I'm curious how to read code effectively. I agree that python code
is clear, but when it becomes long, reading it can still be a hard
work.

BTW. I think this problem also exists in other script languages.

**Stargaming** · Mar 17 '08, 05:55 AM

Re: About reading Python code

On Sun, 16 Mar 2008 20:54:01 -0700, WaterWalk wrote:

Hello. I wonder what's the effective way of figuring out how a piece of
python code works.

If your Python code is well-written, it should be easy figuring out what
it means by just reading it. For more complex programs, of course, this
method can fail.

With C I often find it very useful to be able to run
the code in step mode and set breakpoints in a debugger so I can watch
how the it executes, how the data change and how the code jumps from one
function to another. But with Python, the debugger is a little
primitive. The default IDLE doesn't even allow me to set a breakpoint.
When the code is long, I am often lost in it.

IDLE is just, well, a batteries-included editor. There are many people
(me included) who do *not* like it because it's so weak and doesn't have
any real uses cases if your programs get sufficiently complex (because
IDLE itself is sufficiently primitive).

You might be interested in *real* debuggers, such as the Python Debugger
`PDB <http://docs.python.org/lib/module-pdb.html>`_. If you don't find
its usage obvious, a quick google search just turned up a nice `tutorial
<http://www.ferg.org/papers/debugging_in_py thon.html>`_.

You might find the `Python Profilers <http://docs.python.org/lib/
profile.html>`_ particularly interesting, `profile` for finding out which
function sucks up the most calls/time, `trace` for more sophisticated
stuff.
`pythontracer <http://code.google.com/p/pythontracer/>` sounds like a
good combination of both.

So I'm curious how to read code effectively. I agree that python code is
clear, but when it becomes long, reading it can still be a hard work.

A common practice is just inserting `print` statements since it's so
easy. If you think your debugging isn't temporary but could be useful and
will be enabled every now and then, you could also use the `logging
module <http://docs.python.org/lib/module-logging.html>`_ with the
``DEBUG`` level.

There was a blog post recently about how to do this `generically for
functions <http://wordaligned.org/articles/echo>`_.

BTW. I think this problem also exists in other script languages.

FWIW, I think it's particularly easier in scripting languages to
implement all kinds of tracing (apart from debugging, which is rather
unpopular in Python) because you have one *extra* level (the interpreter)
between your machine and your code.

HTH,
Stargaming

**WaterWalk** · Mar 17 '08, 08:15 AM

Re: About reading Python code

On Mar 17, 1:54 pm, Stargaming <stargam...@gma il.comwrote:

On Sun, 16 Mar 2008 20:54:01 -0700, WaterWalk wrote:

Hello. I wonder what's the effective way of figuring out how a piece of
python code works.

>
If your Python code is well-written, it should be easy figuring out what
it means by just reading it. For more complex programs, of course, this
method can fail.
>

With C I often find it very useful to be able to run
the code in step mode and set breakpoints in a debugger so I can watch
how the it executes, how the data change and how the code jumps from one
function to another. But with Python, the debugger is a little
primitive. The default IDLE doesn't even allow me to set a breakpoint.
When the code is long, I am often lost in it.

>
IDLE is just, well, a batteries-included editor. There are many people
(me included) who do *not* like it because it's so weak and doesn't have
any real uses cases if your programs get sufficiently complex (because
IDLE itself is sufficiently primitive).
>
You might be interested in *real* debuggers, such as the Python Debugger
`PDB <http://docs.python.org/lib/module-pdb.html>`_. If you don't find
its usage obvious, a quick google search just turned up a nice `tutorial
<http://www.ferg.org/papers/debugging_in_py thon.html>`_.
>
You might find the `Python Profilers <http://docs.python.org/lib/
profile.html>`_ particularly interesting, `profile` for finding out which
function sucks up the most calls/time, `trace` for more sophisticated
stuff.
`pythontracer <http://code.google.com/p/pythontracer/>` sounds like a
good combination of both.
>

So I'm curious how to read code effectively. I agree that python code is
clear, but when it becomes long, reading it can still be a hard work.

>
A common practice is just inserting `print` statements since it's so
easy. If you think your debugging isn't temporary but could be useful and
will be enabled every now and then, you could also use the `logging
module <http://docs.python.org/lib/module-logging.html>`_ with the
``DEBUG`` level.
>
There was a blog post recently about how to do this `generically for
functions <http://wordaligned.org/articles/echo>`_.
>

BTW. I think this problem also exists in other script languages.

>
FWIW, I think it's particularly easier in scripting languages to
implement all kinds of tracing (apart from debugging, which is rather
unpopular in Python) because you have one *extra* level (the interpreter)
between your machine and your code.
>
HTH,
Stargaming

Thanks for your informative reply. I'll try them. I think I need more
practice to familiarize myself with those idioms of Python.

**Ben C** · Mar 17 '08, 08:55 AM

Re: About reading Python code

On 2008-03-17, WaterWalk <toolmaster@163 .comwrote:

Hello. I wonder what's the effective way of figuring out how a piece
of python code works. With C I often find it very useful to be able to
run the code in step mode and set breakpoints in a debugger so I can
watch how the it executes, how the data change and how the code jumps
from one function to another. But with Python, the debugger is a
little primitive. The default IDLE doesn't even allow me to set a
breakpoint.

It does, you just right-click and go "set breakpoint". But yes IDLE is a
bit basic.

**Nir** · Mar 17 '08, 09:55 AM

Re: About reading Python code

On Mar 17, 5:54 am, WaterWalk <toolmas...@163 .comwrote:

Hello. I wonder what's the effective way of figuring out how a piece
ofpythoncode works. With C I often find it very useful to be able to
run the code in step mode and set breakpoints in adebuggerso I can
watch how the it executes, how the data change and how the code jumps
from one function to another. But withPython, thedebuggeris a
little primitive. The default IDLE doesn't even allow me to set a
breakpoint. When the code is long, I am often lost in it.
>
So I'm curious how to read code effectively. I agree thatpythoncode
is clear, but when it becomes long, reading it can still be a hard
work.

Try Winpdb - www.winpdb.org (works on Linux as well). Don't forget to
send feedback.

**Roman Dodin** · Mar 17 '08, 10:15 AM

Re: About reading Python code

WaterWalk Ð¿Ð¸ÑˆÐµÑ‚:

Hello. I wonder what's the effective way of figuring out how a piece
of python code works. With C I often find it very useful to be able to
run the code in step mode and set breakpoints in a debugger so I can
watch how the it executes, how the data change and how the code jumps
from one function to another. But with Python, the debugger is a
little primitive. The default IDLE doesn't even allow me to set a
breakpoint. When the code is long, I am often lost in it.
>
So I'm curious how to read code effectively. I agree that python code
is clear, but when it becomes long, reading it can still be a hard
work.
>

You also can use free IDE (for example Eclipse) and PyDev plugin, which
includes comfortable Debugger

**Gabriel Genellina** · Mar 17 '08, 12:05 PM

Re: About reading Python code

En Mon, 17 Mar 2008 01:54:01 -0200, WaterWalk <toolmaster@163 .com>
escribiï¿½:

Hello. I wonder what's the effective way of figuring out how a piece
of python code works. With C I often find it very useful to be able to
run the code in step mode and set breakpoints in a debugger so I can
watch how the it executes, how the data change and how the code jumps
from one function to another. But with Python, the debugger is a
little primitive. The default IDLE doesn't even allow me to set a
breakpoint. When the code is long, I am often lost in it.

See the wiki at http://wiki.python.org/moin/DevelopmentTools for more
editors, debugging tools and IDEs.

--
Gabriel Genellina

**sturlamolden** · Mar 18 '08, 01:05 AM

Re: About reading Python code

On 17 Mar, 04:54, WaterWalk <toolmas...@163 .comwrote:

So I'm curious how to read code effectively. I agree that python code
is clear, but when it becomes long, reading it can still be a hard
work.

First, I recommend that you write readable code! Don't use Python as
if you're entering the obfuscated C contest.

Two particularly important points:

* If you find yourself thinking this module is too long, that's
probably what it is. Half a page of code per module is fine. Two pages
of code per module can be too much.

* Comments are always helpful to the reader.

Second, I recommend getting a good IDE. E.g. pick one of:

* Microsoft Visual Studio (commercial)
* Eclipse with PyDev and CDT (free)
* SPE (free)
* ActiveState Komodo IDE (commercial)

**Paul Rubin** · Mar 18 '08, 01:05 AM

Re: About reading Python code

WaterWalk <toolmaster@163 .comwrites:

from one function to another. But with Python, the debugger is a
little primitive. The default IDLE doesn't even allow me to set a
breakpoint. When the code is long, I am often lost in it.

Try winpdb.org which despite the name has nothing to do with MS Windows.

**hellt** · Mar 18 '08, 07:05 AM

Re: About reading Python code

On 18 ÍÁÒ, 03:57, sturlamolden <sturlamol...@y ahoo.nowrote:

On 17 Mar, 04:54, WaterWalk <toolmas...@163 .comwrote:
>

So I'm curious how to read code effectively. I agree that python code
is clear, but when it becomes long, reading it can still be a hard
work.

>
First, I recommend that you write readable code! Don't use Python as
if you're entering the obfuscated C contest.
>
Two particularly important points:
>
* If you find yourself thinking this module is too long, that's
probably what it is. Half a page of code per module is fine. Two pages
of code per module can be too much.
>
* Comments are always helpful to the reader.
>
Second, I recommend getting a good IDE. E.g. pick one of:
>
* Microsoft Visual Studio (commercial)
* Eclipse with PyDev and CDT (free)
* SPE (free)
* ActiveState Komodo IDE (commercial)

under Microsoft Visual Studio do you mean IronPython instance?

**sturlamolden** · Mar 18 '08, 02:15 PM

Re: About reading Python code

On 18 Mar, 08:00, hellt <Dodin.Ro...@gm ail.comwrote:

under Microsoft Visual Studio do you mean IronPython instance?

AFAIK, with the latest VS 2008 you can develop for CPython and
IronPython.

Haibo Luo's weblog

http://blogs.msdn.com/haibo_luo/archive/2007/10/16/5482940.aspx

**Phil** · Mar 25 '08, 02:35 PM

Re: About reading Python code

On 2008-03-18, sturlamolden <sturlamolden@y ahoo.nowrote:

First, I recommend that you write readable code! Don't use Python as
if you're entering the obfuscated C contest.
>
Two particularly important points:
>
* Comments are always helpful to the reader.

It would be nice if this was the case! I once saw a preogram where
a line of code like this:

foo++;

Would be annotated with a comment like this:

/*************** *************** *************** *******/
/* */
/* Increment foo */
/* */
/*************** *************** *************** *******/

This comment was worse than useless, because it (and others like
it) took up space that distracted from the information-containing
parts of the code.