how to count substring in a string in python

1string.count(substring, start, end)
2# Start and end is optional

1count = string.count(substring)

1def count_substring(string,sub_string):
2    l=len(sub_string)
3    count=0
4    for i in range(len(string)-len(sub_string)+1):
5        if(string[i:i+len(sub_string)] == sub_string ):      
6            count+=1
7    return count  
8