Number of occurrences of a substring in a string

Question

I need to count the nunber of times the substring \'bob\' occurs in a string.

Example problem: Find the number of times \'bob\' occurs in string s such

Answer 1

def count_substring(string, sub_string):
count=a=0
while True:
    a=string.find(sub_string)
    string=string[a+1:]
    if a>=0:
        count=count+1;
    else:
        break
return count