Are there Python packages for Landsat 8 processing?

I just thought I'd add that there are some 'pure' Python solutions for several nodes in this workflow, also.

Some file reading and basic processing:

Spectral Python: http://spectralpython.sourceforge.net/

More classification than you'll find in pure remote sensing and GIS packages:

http://scikit-learn.org/stable/

More links I can't share: 6S Python atmospheric correction, Shapely, gdal bindings for reading geoTIFF (relatively trivial to parse metadata from Landsat 8 and read all images into a cube). There are other processing options in SciPy general and MDP (modular data processing, too).

If you really want to use python, and you need functionality similar to GRASS, perhaps the easiest solution would be to use GRASS via Python.

That isn't specific to Landsat8, but I don't think a processing solution should be tied that closely to a specific satellite. You could implement some simple wrappers / higher level functions if you're consistently performing the same operations.

Side note: on "Cloud identification", remember that Landsat8 has a specific sensor for this (Band 9 on OLI) so that should be pretty trivial.