[issue21253] Difflib.compare() crashes on mostly different sequences

[Gregory P. Smith]

Gregory P. Smith added the comment:

It appears to devolve into linear recursion in this case, one per each item in one of the sequences being searched for a match, so even using a stack seems wrong as it'd still be linear (though it would prevent the recursion depth problem).

The mutual _fancy_replace + _fancy_helper linear recursion comes from http://hg.python.org/cpython/file/604b74f9a07d/Lib/difflib.py#l1021

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