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

The current best answer involving method count doesn't really count for overlapping occurrences and doesn't care about empty sub-strings as well. For example:

>>> a = 'caatatab'
>>> b = 'ata'
>>> print(a.count(b)) #overlapping
1
>>>print(a.count('')) #empty string
9

The first answer should be 2 not 1, if we consider the overlapping substrings. As for the second answer it's better if an empty sub-string returns 0 as the asnwer.

The following code takes care of these things.

def num_of_patterns(astr,pattern):
    astr, pattern = astr.strip(), pattern.strip()
    if pattern == '': return 0

    ind, count, start_flag = 0,0,0
    while True:
        try:
            if start_flag == 0:
                ind = astr.index(pattern)
                start_flag = 1
            else:
                ind += 1 + astr[ind+1:].index(pattern)
            count += 1
        except:
            break
    return count

Now when we run it:

>>>num_of_patterns('caatatab', 'ata') #overlapping
2
>>>num_of_patterns('caatatab', '') #empty string
0
>>>num_of_patterns('abcdabcva','ab') #normal
2