Given a function:
def A(a, b, c): a *= 2 b *= 4 c *= 8 return a+b+c
How can I set the \'c\' var to be called-by-reference,
You can't. Python cannot do that.
What you can do is pass a wrapper that has __imul__() defined and an embedded int, and the augmented assignment will result in the embedded attribute being mutated instead.
__imul__()
int