Calling a function with unknown arguments?

[Rob]

I can get a list of a function's arguments.
>>> def bob(a, b):
...     return a+b
...
>>> bob.func_code.co_varnames
('a', 'b')

Let's say that I also have a dictionary of possible arguments for this
function.
>>> possible = {'a':10, 'b':5, 'c':-3}

How do I proceed to call bob(a=10, b=5) with this information?

Thanks!