How Can I Count Substring Occurrences in Python, Including Overlapping Instances?

Determining Substring Frequency Within a String

In Python, counting the occurrences of a particular substring within a string is a common task. Here's how you can achieve this:

Using string.count()

The str.count(substring) method provides a straightforward approach to counting substring occurrences. It returns the number of non-overlapping instances of substring within the string. For example:

>>> 'foo bar foo'.count('foo')
2

This method effectively traverses the string and increments a counter each time it encounters the specified substring. However, it's crucial to note that it only considers non-overlapping occurrences.

Achieving Overlapping Substring Count

If you require the count of overlapping substrings, you'll need to explore alternative approaches. One option is to leverage the power of regular expressions:

import re

pattern = re.compile('(substring)')
count = len(re.findall(pattern, 'this is a substring test'))

This method utilizes a regular expression pattern to match all occurrences of the substring, including overlapping ones. It captures the matches as a list and returns the count.

Conclusion

Whether it's counting non-overlapping or overlapping substring occurrences, the str.count() method and regular expressions provide effective solutions for this common programming task.

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