Micropython or minimal python installation

Micro Python is actively maintained and has been ported to a bunch of microcontrollers.

For other small implementations, you might also want to check out tinypy or PyMite.

If you don't care about size, but really just want an easy way to distribute a python program, consider PyInstaller or one of the others on this list.

Portable python might do what you want. It's a python installation for USB thumb drives.

There's now finally Micro Python, claiming to be full reimplementation of Python 3 core, fitting even into medium-size 32bit microcontrollers. API will be different of course, so C modules will require porting. Project is funded via KickStarter, source code will be released some time after the campaign (request for consideration was made to author to not delay release of the source, to help bootstrap Micro Python community sooner).

http://micropython.org/