Consider the following code:
def fac(m):
    def iter(acc,n):
        if n <= 0 :
            return acc
        else:
            return iter(acc * n, n - 1)
    return iter(1,m)

#When called wtih a large parameter, you get exceed the recursion limit

fac(10000)

In a future release, I suggest updating the interpreter and byte code compiler to handle tail recursion properly as in scheme.

This sort of optimization is one of the many that aren't possible without changing the semantics of the language.  Recursive calls use a LOAD_GLOBAL in the function to reference itself.  The value of that global is subject to change outside the body of the function.