Count number of occurrences of a substring in a string

Question

string.count(substring), like in:

>>> "abcdabcva".count("ab")
2

Update:

As pointed up in the comments, this is the way to do it for non overlapping occurrences. If you need to count overlapping occurrences, you'd better check the answers at: "Python regex find all overlapping matches?", or just check my other answer below.

s = 'arunununghhjj'
sb = 'nun'
results = 0
sub_len = len(sb)
for i in range(len(s)):
    if s[i:i+sub_len] == sb:
        results += 1
print results

Depending what you really mean, I propose the following solutions:

1. You mean a list of space separated sub-strings and want to know what is the sub-string position number among all sub-strings:

   s = 'sub1 sub2 sub3'
   s.split().index('sub2')
   >>> 1
   

2. You mean the char-position of the sub-string in the string:

   s.find('sub2')
   >>> 5
   

3. You mean the (non-overlapping) counts of appearance of a su-bstring:

   s.count('sub2')
   >>> 1
   s.count('sub')
   >>> 3
   

The best way to find overlapping sub-string in a given string is to use the python regular expression it will find all the overlapping matching using the regular expression library. Here is how to do it left is the substring and in right you will provide the string to match

print len(re.findall('(?=aa)','caaaab'))
3

To find overlapping occurences of a substring in a string in Python 3, this algorithm will do:

def count_substring(string,sub_string):
    l=len(sub_string)
    count=0
    for i in range(len(string)-len(sub_string)+1):
        if(string[i:i+len(sub_string)] == sub_string ):      
            count+=1
    return count  

I myself checked this algorithm and it worked.