Why is count() method giving strange answer?

Question

s = "ANANAS"
print(s.count("ANA"))
print(s.count("AN"))
print(s.count("A"))

"ANA" occurs two times in "ANANAS" but python prints 1 whereas "AN" occurs two times and python prints 2. "A" occurs three times and python prints 3 as output. Why is this strange behaviour?

score 1 · Accepted Answer · answered Apr 17 '19 at 05:55

1

Straight from the documentation:

str.count(sub[, start[, end]])
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.

The two occurences of "ANA" in "ANANAS" are overlapping, hence s.count("ANA") only returns 1.

answered Apr 17 '19 at 05:55

glhr

4,439
1
15
26

then how to use count() when there is a overlap – raviTeja Apr 17 '19 at 06:00
`count()` is not the right tool for the job here. See [this post](https://stackoverflow.com/questions/2970520/string-count-with-overlapping-occurrences) which shows different ways of counting overlapping sub-strings. – glhr Apr 17 '19 at 06:02

score 1 · Answer 2 · answered Apr 17 '19 at 06:32

This is because in your sub string ANA will be only counted twice if it's something like "testANAANAAN " I.e two full occurrences of ANA . As, in your case if it already checked first full substring it will not use that string part again from full string and will look for matching substring in rest of string.

Why is count() method giving strange answer?

2 Answers2