As of 0c6f12a (26 Feb 2013), Matplotlib on Python 2.0 requires pyparsing 1.5.6 or higher. Unfortunately, Ubuntu 12.04 LTS (the most recent long-term support release of Ubuntu) only has pyparsing 1.5.2, so it would be desirable to lower the minimum required version in order to be able to run the latest version of Matplotlib on Ubuntu LTS without having to manually install other libraries.

I have edited the pyparsing version requirement in __init__.py from 1.5.6 to 1.5.2 and run the test suite against pyparsing 1.5.2 included with Ubuntu 12.04. All of the tests still pass. Was there a good reason to set it to 1.5.6, or was it just the version you happened to have handy to test with? Unless there is a good reason, I recommend lowering the minimum version to 1.5.2.