Overlapping count of substring in a string in Python

Question

I want to find all the counts (overlapping and non-overlapping) of a sub-string in a string. I found two answers one of which is using regex which is not my intention and t

Answer 1

A brute-force approach is just

n = len(needle)
count = sum(haystack[i:i+n] == needle for i in range(len(haystack)-n+1))

(this works because in Python True and False are equivalent to numbers 1 and 0 for most uses, including math).

Using a regexp instead it could be

count = len(re.findall(needle[:1]+"(?="+re.escape(needle[1:])+")",
                       haystack))

(i.e. using a(?=ba) instead of aba to find overlapping matches too)