Count number of occurrences of a given substring in a string

Question

How can I count the number of times a given substring is present within a string in Python?

For example:

>>> \'foo bar foo\'.numberOfOccurre         


        

Answer 1

I will keep my accepted answer as the "simple and obvious way to do it" - however, that does not cover overlapping occurrences. Finding out those can be done naively, with multiple checking of the slices - as in: sum("GCAAAAAGH"[i:].startswith("AAA") for i in range(len("GCAAAAAGH")))

(which yields 3) - it can be done by trick use of regular expressions, as can be seen at Python regex find all overlapping matches? - and it can also make for fine code golfing - This is my "hand made" count for overlappingocurrences of patterns in a string which tries not to be extremely naive (at least it does not create new string objects at each interaction):

def find_matches_overlapping(text, pattern):
    lpat = len(pattern) - 1
    matches = []
    text = array("u", text)
    pattern = array("u", pattern)
    indexes = {}
    for i in range(len(text) - lpat):
        if text[i] == pattern[0]:
            indexes[i] = -1
        for index, counter in list(indexes.items()):
            counter += 1
            if text[i] == pattern[counter]:
                if counter == lpat:
                    matches.append(index)
                    del indexes[index]
                else:
                    indexes[index] = counter
            else:
                del indexes[index]
    return matches

def count_matches(text, pattern):
    return len(find_matches_overlapping(text, pattern))