Python string count not working properly?

2
votes

There are two occurrences of 'aba' in 'ababa' (0th index and 2nd index):

myString = 'ababa'
print(myString.count('aba'))

Yet this code outputs a value of: 1
I know this issue seems really simple, but shouldn't the answer be 2 here?
If not, then isn't the count function not really doing what it's supposed to?

Is there a simple alternative?

2
pythonstringfunctioncount
It is correct. ababa - aba = ba. ba is not aba. So thats 1. - Moon Cheesez
There's also this: stackoverflow.com/questions/2970520/… - Headcrab
if you did "a".count("a") would you expect infinity as the count? Why not? - TessellatingHeckler

2 Answers

9
votes

From the Python string function documentation

Return the number of non-overlapping occurrences of substring sub in the range [start, end]. Optional arguments start and end are interpreted as in slice notation.

count does not count overlapping occurrences.

If you want to count overlapping occurrences you can use regex with a lookahead assertion:

import re
print(len(re.findall('(?=aba)', 'ababa')))
2
votes

Documentation to the rescue: https://docs.python.org/2/library/string.html

Return the number of (non-overlapping) occurrences of substring sub in string s[start:end]. Defaults for start and end and interpretation of negative values are the same as for slices.