Python Power function
return means "Eureka! I have found the answer! It is …."  It hands that result back to the caller and stops executing any more code in this function.

Unlike x**y, your function gives incorrect results for negative or non-integer values of y.  You should note that caveat in a docstring.

The standard way to do counting loops in Python is to use range() (or, in Python 2, xrange()).

To reduce the complexity of your code, you should avoid unnecessary special cases.

def pow(x, y):
    """Raise x to the power y, where y must be a nonnegative integer."""
    result = 1
    for _ in range(y):   # using _ to indicate throwaway iteration variable
        result *= x
    return result




This particular looping pattern (starting with some initial value and repeatedly applying an operation to the result) could be reduced to a one-liner:

from functools import reduce  # Optional in Python 2, required in Python 3

def pow(x, y):
    """Raise x to the power y, where y must be a nonnegative integer."""
    return reduce(lambda result, _: result * x, range(y), 1)


This solution is admittedly foreign-looking to a C programmer.  The reduce() function uses 1 as the starting value (equivalent to result = 1 in the first solution).  For each _ in range(y), it does result = result * x.  lambda is just a way to define a simple function on the spot.



A more efficient algorithm would be repeated squaring.