A cross-platform uptime for the Python. To install it, just do:

$ pip install uptime

Assuming you have pip installed. If you don't, a tarball is also available.

Then just use it like this:

from uptime import uptime

print uptime()

Or run the module as a script:

$ python -m uptime
Uptime: 109 days, 33.84 seconds.
$ python -m uptime -b
Booted: Wed Oct 10 06:28:24 2012 CET.

(You may need to use uptime.__main__, depending on your version of Python.)

Full documentation here. Works with any version of Python from 2.5 on, including Python 3.

Tested on a bunch of platforms, expected to work on a bunch more. See the documentation for details.

For a list of platforms I'm working on adding, see here. Know any others I should add? Let me know.