Beginning Python - From Novice to Professional

214 CHAPTER 10 ■ BATTERIES INCLUDED
You now have a precise description of the range function, and because you probably had
the Python interpreter running already (wondering about functions like this usually happens
while you are programming), accessing this information took just a couple of seconds.
However, not every module and every function has a good docstring (although it should),
and sometimes you may need a more thorough description of how things work. Most modules
you download from the Web have some associated documentation. In my opinion, some of the
most useful documentation for learning to program in Python is the Python Library Reference,
which describes all of the modules in the standard library. If I want to look up some fact about
Python, nine times out of ten, I find it there. The library reference is available for online browsing
(at http://python.org/doc/lib) or for download, as are several other standard documents
(such as the Python Tutorial, or the Python Language Reference). All of the documentation is
available from the Python Web site, at http://python.org/doc.
Use the Source
The exploration techniques I’ve discussed so far will probably be enough for most cases. But
those of you who wish to truly understand the Python language may want to know things about
a module that can’t be answered without actually reading the source code. Reading source
code is in fact one of the best ways to learn Python—besides coding yourself.
Doing the actual reading shouldn’t be much of a problem, but where is the source? Let’s
say you wanted to read the source code for the standard module copy. Where would you find it?
One solution would be to examine sys.path again, and actually look for it yourself, just like the
interpreter does. A faster way is to examine the module’s __file__ property:
>>> print copy.__file__
C:\Python24\lib\copy.py
■Note If the file name ends with .pyc, just use the corresponding file whose name ends with .py.
There it is! You can open the copy.py file in your code editor (for example, IDLE) and start
examining how it works.
■Caution When opening a standard library file in a text editor like this, you run the risk of accidentally
modifying it. Doing so might break it, so when you close the file, make sure that you don’t save any changes
you might have made.
Note that some modules don’t have any Python source you can read. They may be built
into the interpreter (such as the sys module) or they may be written in the C programming
language. (The C source code is also available, but that’s beyond the scope of this book. See
Chapter 17 for more information on extending Python using C.)