IndentationError unindent does not match any outer indentation level

Question

When I compile  my python code I am getting this error

My code:

import sys

def Factorial(n): # Return factorial
    result = 1
    for i in range (1,n):
        result = result * i
    print "factorial is ",result
    return result

This is the error I am getting:

IndentationError: unindent does not match any outer indentation level

Can someone please explain to me why this error occurred? and how can I solve this?