How to comment code?

James Stroud jstroud at
Fri Jan 19 23:07:56 CET 2007

Martin P. Hellwig wrote:
> Hi all,
> I've been toying with python for about two years now. Not every day, 
> just when I encounter something in my job (sysadmin) repetitively dull.
> The amazing thing is that like any other language (natural or not) 
> learning it more gives you power to express your thoughts better and 
> create something from nothing, for me this is something I can only 
> compare to freedom.
> However since I'm learning more of python I've struggled with 
> commenting, how should I've comment my code? I'm not talking about the 
> style but more on the concept itself, things that where a couple of 
> month ago a bunch of monkey poop is now as easy as reading a comic.
> I always give a brief description on what the code is supposed to do and 
>  I suppose that any serious coder knows way more then me about 
> programming so I don't bother to comment that much since it mostly (in 
> my eyes) just clutters up the code and makes it actually harder to read.
> Though this makes me uncomfortably, commenting so little, I was thinking 
> that perhaps something like doctest (I'm not so much into unit testing 
> or the equivalents at this moment) has the side affect to make my code 
> more understandable and readable. Any practical experience you'd like to 
> share with me, any other comments are welcome too of course :-)

I have found it useful to familiarize myself some tool such as epydoc 
and write comments in the function doc-string. For example,

def doit(stuff, beta, cycles):
   Does nothing with I{stuff} in an infinite loop by applying a null
   operation. The I{cycles} parameter is multiplied by infinity.

   @param beta: null operator not to be applied to stuff
   @type beta: callable
   @type cycles: int

This explains paramaters, etc., for you and other users of your API and 
paves the way for automatically generated documentation. Note that it 
would be excessive to comment each and every parameter, etc. Once the 
code is working correctly, a lot of in-line comments can be removed. 
Usually, in python, correctly working code is self explanatory at the 
implementation level, especially if you attempt to code "pythonically" 
(which can roughly be defined as the best practices according to the 
python community or the community subset who post to comp.lang.python).

If you find that your code gets very complicated and needs excessive 
commenting to understand, try to factor it into hierarchically related 
simpler functions and classes and comment each individually using 
doc-strings. In essence, think about commenting the interface rather 
than the implementation.

Use module level doc-strings (comments) to gather usage and explanation 
  notes for the most useful functions. This allows users (for example, 
you) to use your libraries without burrowing into the automatically 
generated documentation for each and every function.

Other tools may be as useful as epydoc, but this is the general strategy 
I have converged upon.


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