You can install this plugin, Python Shell into Chrome. Here's some info from that extensions info page in the store:
Python shell for your browser.
A Python shell for Chrome.
- Python 2.7
- Ruby 1.8
These are the only languages that have been currently compiled to
Alternatively you can go put your device in Developer Mode and gain access to a shell from where you can install/launch Python.
Lastly you can check out the Skulpt Interpreter. Main site's here.
Skulpt is an entirely in-browser implementation of Python.
You can install a full fledged Linux on the Chromebook hardware using the project Crouton.
crouton is a set of scripts that bundle up into an easy-to-use,
Chromium OS-centric chroot generator. Currently Ubuntu and Debian are
supported (using debootstrap behind the scenes), but "Chromium OS
Debian, Ubuntu, and Probably Other Distros Eventually Chroot
Environment" doesn't acronymize as well (crodupodece is admittedly
pretty fun to say, though).
There's a easy to follow tutorial on Life Hacker which walks you through the installation and setup, titled: How to Install Linux on a Chromebook and Unlock Its Full Potential.
Which way to go?
If you're serious about using the Chromebook hardware as a development box I would go with Crouton. The other options only give you pieces of Python. If you're serious about doing any real development this is really the only option.