This is a python interface to giac. It simulates a giac session. As simple as it gets:
import pygiac
g = pygiac.GiacSession()
print g.compute('2+2')
print g.compute('p := factor(a^2-b^2)')
print g.compute('expand(p)')
Eventually, it should be platform independent; at the moment it works on windows; linux version may need some minor modifications.
If launched from command line, it simulates giac command line interaction (note that giac.exe does not work in windows' command line).
See __init__ for details. See __main__ for some examples.

Download here. See also castex, a python script that compiles a latex document including giac computations and plots.

Remarks, questions?