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Asked: 2026-05-11T02:09:42+00:00

This is a generalization of the string contains substring problem to (more) arbitrary types.

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This is a generalization of the ‘string contains substring’ problem to (more) arbitrary types.

Given an sequence (such as a list or tuple), what’s the best way of determining whether another sequence is inside it? As a bonus, it should return the index of the element where the subsequence starts:

Example usage (Sequence in Sequence):

>>> seq_in_seq([5,6],  [4,'a',3,5,6]) 3 >>> seq_in_seq([5,7],  [4,'a',3,5,6]) -1 # or None, or whatever

So far, I just rely on brute force and it seems slow, ugly, and clumsy.

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  1. I second the Knuth-Morris-Pratt algorithm. By the way, your problem (and the KMP solution) is exactly recipe 5.13 in Python Cookbook 2nd edition. You can find the related code at http://code.activestate.com/recipes/117214/

    It finds all the correct subsequences in a given sequence, and should be used as an iterator:

    >>> for s in KnuthMorrisPratt([4,'a',3,5,6], [5,6]): print s 3 >>> for s in KnuthMorrisPratt([4,'a',3,5,6], [5,7]): print s (nothing)
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