What python packages are installed?

Work at Google on a team that works primarily in python has pushed me to get tons better at python. It's one thing to know and working a language. It's a whole nother thing to get to that expert level. I have been trying to figure out how to get others the hard won knowledge that makes for amazing python. The is always the danger of getting overly clever and writing code that is difficult to understand. Writing and managing python packages is an area that I have felt like was too difficult. I finally feel like I am starting to break through some of the confusion. This might not be the right thing in the long run with python 3 working on a new distribution package, but with the advent of the distribute package (a fork of setuptools), I'm feeling more comfortable.

I few years ago, I discovered the python module yolk (https://github.com/cakebread/yolk). This is a nice module that makes it easy to ask questions about your python install from the command line.

virtualenv test-ve
source test-ve/bin/activate
pip install yolk
yolk --list
Python          - 2.7.3        - active development (/sw/lib/python2.7/lib-dynload)
pip             - 1.2.1        - active 
setuptools      - 0.6c11       - active 
wsgiref         - 0.1.2        - active development (/sw/lib/python2.7)
yolk            - 0.4.3        - active

# "yolk -U" or
yolk --show-updates
No newer packages found at The Cheese Shop

Going back to my normal python environment, you can see a list of packages that are out of date:

yolk -U | head
 Cython 0.16 (0.18)
 Pygments 1.5 (1.6)
 SQLAlchemy 0.7.9 (0.7.10)
 Shapely 1.2.16 (1.2.17)
 distribute 0.6.34 (0.6.35)
 docutils 0.8 (0.10)
 logilab-common 0.58.3 (0.59.0)
 Mercurial 2.4.2 (2.5.1)
 mock 0.7.0b3 (1.0.1)
 numexpr 1.4.2 (2.0.1)

That's nice, but I've blogged about yolk before and it would be better to know how to do this kind of thing from within python. What if I want to list which packages I have installed from within an IPython notebook to document the state of the world that I used? I'd like the names of all python modules as found in pypi and the versions of a few critical packages.

deactivate # drop out of test-ve
virtualenv --system-site-packages test2-ve
source test2-ve/bin/activate
pip install bigquery # This is Google's BigQuery python interface.
ipython notebook --pylab=inline

And now, how do I ask about packages in the notebook?

import pkg_resources
 
pkgs = [pkg for pkg in pkg_resources.Environment()]
len(pkgs)

pkgs[:10]
['configobj',
 'logilab-astng',
 'shapely',
 'pyproj',
 'distribute',
 'yolk',
 'python-dateutil',
 'pygments',
 'mysql-python',
 'numexpr']

bq_version = pkg_resources.get_distribution('bigquery').version
bq_version

'2.0.12'

pkg_resources.parse_version(version)
('00000002', '00000000', '00000012', '*final')

So, I'm using version 2.0.12 of the BigQuery python module.