gh-150821: Skip URL parsing in mimetypes.guess_type() for file paths#150828
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gh-150821: Skip URL parsing in mimetypes.guess_type() for file paths#150828gaborbernat wants to merge 1 commit into
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…paths guess_type() parsed every argument as a URL before checking the extension, even for plain file paths that have no scheme. Detect the no-scheme case and go straight to extension lookup, avoiding urlparse() and its lazy import. Real URLs keep the full parsing path; results are unchanged.
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sobolevn
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Jun 3, 2026
| # A URL scheme requires a ':'; a plain file path (the common case) has | ||
| # none, so skip the relatively expensive urlparse() for it. | ||
| if isinstance(url, str) and ':' not in url: | ||
| return self.guess_file_type(url, strict=strict) |
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| return self.guess_file_type(url, strict=strict) | |
| return self.guess_file_type(url, strict=strict) | |
style nit :)
| scheme = p.scheme | ||
| url = p.path | ||
| else: | ||
| return self.guess_file_type(url, strict=strict) |
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question: can this branch still happen now? do we have tests for this case?
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| # A URL scheme requires a ':'; a plain file path (the common case) has | ||
| # none, so skip the relatively expensive urlparse() for it. |
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This isn't strictly true, : is accepted on Linux, e.g.:
$ touch fi:le
$ realpath fi\:le
/tmp/fi:le
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mimetypes.guess_type()accepts either a URL or a filesystem path, so it parses its argument as a URL withurllib.parse.urlparse()before looking at the extension. The common argument is a plain file path, which has no URL scheme to find, so the parse — and theurllib.parseimport it triggers — is spent on nothing. Guessing content types from file names is everywhere: static-file servers, upload handlers, archive and build tools deciding how to treat each file as they walk a tree of thousands.A URL scheme requires a
:, so a path without one cannot be a URL. This detects that case and goes straight to extension lookup, skippingurlparse()and its lazy import. Real URLs, and the rare path that contains a:, still take the full parsing path, and results are unchanged for both.Guessing types for 15 real file names sampled from the top-1000 corpus improves from 23.4 µs to 11.0 µs, 112% faster.
Benchmark (pyperf)
Run base vs patched by swapping
Lib/mimetypes.pyon the same interpreter. The names are real file names sampled from the top-1000 corpus.Resolves #150821.