By: Andrew Williams, Technical Support Engineeer

When working with an open source library, sometimes the best documentation is the source code itself. Here’s a quick shell function for finding the code you’re looking for in the Python scripting language. Simply add these three lines to your .bash_profile or .bashrc file.

**

function pycd () {

cd `python -c “import os.path, $1; print os.path.dirname($1.__file__)”`

}

**

Now you can you use the ‘pycd’ command to change to the directory the module lives inside. Simply specify the module you’re looking for as an argument. Here is an example using the popular “lxml” module.

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contegix@AJW-Contegix-MBP:~$ pycd lxml

contegix@AJW-Contegix-MBP:lxml$ pwd

/Library/Python/2.6/site-packages/lxml-2.2.6-py2.6-macosx-10.6-universal.egg/lxml

andrew@andrew-mbp:lxml$ ls

ElementInclude.py  _elementpath.py    cssselect.py       etree.py           objectify.py       pyclasslookup.pyc  usedoctest.pyc

ElementInclude.pyc _elementpath.pyc   cssselect.pyc      etree.pyc          objectify.pyc      sax.py

__init__.py        builder.py         doctestcompare.py  etree.so           objectify.so       sax.pyc

__init__.pyc       builder.pyc        doctestcompare.pyc html               pyclasslookup.py   usedoctest.py

**

The Python one-liner is pretty simple. It first imports the ‘os.path’ module and then the module that you specified on the command line (We’ll call this the “example” module). It then finds the parent directory of the example module by using the built-in attribute ‘__file__’. This special attribute is a string of the pathname of the file from which the module was loaded. The example module’s parent directory is then written to standard out where the shell expands it for use with the ‘cd’ command.

This command works with both modules in the standard library and with third party libraries. The only caveat is that this will not work with code that is still contained inside a “.egg” package as it’s not actually a directory on the file system.