Possible bug in str.count

Python Help
1 
Python 3.12.1
>>> s = "adada"                                                                                             
>>> s.count("ada")                                                        
>>> 1

Is this expected behavior?

2

Yes, because the documentation says (emphasis added):

Return the number of non-overlapping occurrences of substring sub in the range [start, end].

1 Like
3

Yes, the result is the number of non-overlapping occurrences.

1 Like
4

Thanks, but why is it made so? Like the expected answer by common logic should be 2. What’s the motivation behind such design? Also KMP would also give 2 in O(n + m). Is there another method for count with overlap? This can cause serious bugs.

1 Like
5

The typical workaround is to use a lookahead regex search instead:

import re

assert len(re.findall('(?=ada)', 'adada')) == 2
6

Thanks for that though my question is not regarding how we can do it but rather why is such design there.

7

That depends on the question you ask.
If the question is “how many occurrences can be removed?”
Then 2 is the wrong answer.

4 Likes
8

Only if you disregard the documented behavior. If you expect overlapping matches to be counted, you need to look for a different function.

2 Likes
9

Thanks, I never looked from the following perspective.

10

One can remove simultaneously or sequentially. Both interpretations would still fit.