gh-150821: Skip URL parsing in mimetypes.guess_type() for file paths

gaborbernat · gaborbernat · commit 175764e62cfa · 2026-06-02T16:44:54.000-07:00
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.
diff --git a/Lib/mimetypes.py b/Lib/mimetypes.py
@@ -123,10 +123,14 @@ def guess_type(self, url, strict=True):
         """
         # Lazy import to improve module import time
         import os
-        import urllib.parse
 
         # TODO: Deprecate accepting file paths (in particular path-like objects).
         url = os.fspath(url)
+        # 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)
+        import urllib.parse
         p = urllib.parse.urlparse(url)
         if p.scheme and len(p.scheme) > 1:
             scheme = p.scheme
diff --git a/Misc/NEWS.d/next/Library/2026-06-02-15-45-02.gh-issue-150821.yKimWm.rst b/Misc/NEWS.d/next/Library/2026-06-02-15-45-02.gh-issue-150821.yKimWm.rst
@@ -0,0 +1,2 @@
+Speed up :func:`mimetypes.guess_type` for plain file paths by skipping URL
+parsing when the argument has no scheme. Patch by Bernát Gábor.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Speed up :func:`mimetypes.guess_type` for plain file paths by skipping URL
	`2`	`+parsing when the argument has no scheme. Patch by Bernát Gábor.`