[issue40480] "fnmatch" exponential execution time
kleshni added the comment:
>So the solution is to replace multiple asterisks with a single one
No, this is not a solution. This glob also hangs:
fnmatch.fnmatchcase("a" * 32, "*a" * 16 + "b")
And again, Bash and SQLite 3 work perfectly.
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[issue40480] "fnmatch" exponential execution time
New submission from kleshni :
Hello. The following code hangs:
import fnmatch
fnmatch.fnmatchcase("a" * 32, "*" * 16 + "b")
Measurements show that its execution time rises exponentially with the number
of asterisks. Bash and SQLite 3 process this glob instantly.
This is because "fnmatchcase" generates a regular expression with repeated dots:
(?s:.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*b)\\Z
It's equivalent to:
(?s:.*b)\\Z
But works in exponential time. So the solution is to replace multiple asterisks
with a single one, so the latter regexp is generated instead.
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components: Library (Lib)
messages: 367963
nosy: kleshni
priority: normal
severity: normal
status: open
title: "fnmatch" exponential execution time
type: performance
versions: Python 3.8
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