[python] How many times a substring occurs

If you want to find out the count of substring inside any string; please use below code. The code is easy to understand that's why i skipped the comments. :)

string=raw_input()
sub_string=raw_input()
start=0
answer=0
length=len(string)
index=string.find(sub_string,start,length)
while index<>-1:
    start=index+1
    answer=answer+1
    index=string.find(sub_string,start,length)
print answer