How to Discover Common Substrings in Python using difflib?

Discovering Common Substrings with Python's DiffLib

Comparing two strings to identify their common substring is a fundamental task in string manipulation. This comprehensive guide showcases a Python-based solution utilizing the difflib module to perform this operation efficiently.

Using difflib's Find_Longest_Match Method

The difflib module, part of Python's standard library, provides an array of sequence-comparison utilities. Among them, find_longest_match finds the longest common substring between two strings.

Consider two strings:

string1 = "apple pie available"
string2 = "come have some apple pies"

To find their common substring using find_longest_match:

from difflib import SequenceMatcher

match = SequenceMatcher(None, string1, string2).find_longest_match()

print(match)  # -> Match(a=0, b=15, size=9)
print(string1[match.a:match.a + match.size])  # -> apple pie
print(string2[match.b:match.b + match.size])  # -> apple pie

In this example, the output is:

Match(a=0, b=15, size=9)
apple pie
apple pie

This indicates that the longest common substring is "apple pie," and both strings share this substring.

Compatibility with Python Versions

For Python versions prior to 3.9, the find_longest_match() method requires slightly different arguments:

SequenceMatcher(None, string1, string2).find_longest_match(0, len(string1), 0, len(string2))

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