Question

Using win7 64, python 2.7.2. Code:
def sqrt(x):
"""Returns the square root of x, if x is a perfect square. Prints an error message and returns None otherwise"""
ans = 0
if x >= 0:
while ans*ans < x: ans = ans + 1
if ans*ans != x:
print x, 'is not a perfect square'
return None
else: return ans
else:
print x, 'is a negative number'
return None
When I invoke function:
Traceback (most recent call last):
File "", line 1, in sqrt(16) NameError: name 'sqrt' is not defined