How Can Python's Regular Expressions Find Overlapping Matches?

Overlapping Matches with Regular Expressions in Python

Finding all occurrences of a pattern, even when they overlap, can be a challenge. However, utilizing the power of regular expressions, you can solve this problem effortlessly.

For instance, suppose you need to extract every 10-digit series of numbers from a larger numeric string. Instead of restricting yourself to non-overlapping matches, you can embrace overlaps to gather a complete list.

To achieve this, the key is to employ a capturing group within a lookahead. The lookahead will capture the desired sequence of interest, but since the actual match is the zero-width substring before the lookahead, the matches remain non-overlapping.

import re

s = "123456789123456789"
matches = re.finditer(r'(?=(\d{10}))', s)
results = [int(match.group(1)) for match in matches]

print(results)  # [1234567891, 2345678912, 3456789123, ...]

This approach will yield a list containing the overlapping matches, allowing you to capture every instance of the specified digit sequence in the original string.

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