fix a silly problem of caching gone wrong #5401

Lib/mimetypes.py

@@ -237,6 +237,7 @@ def guess_type(url, strict=True):
     Optional `strict' argument when false adds a bunch of commonly found, but
     non-standard types.
     """
+    if not inited:
         init()
     return guess_type(url, strict)
 
@@ -254,6 +255,7 @@ def guess_all_extensions(type, strict=True):
     Optional `strict' argument when false adds a bunch of commonly found,
     but non-standard types.
     """
+    if not inited:
         init()
     return guess_all_extensions(type, strict)
 
@@ -269,6 +271,7 @@ def guess_extension(type, strict=True):
     Optional `strict' argument when false adds a bunch of commonly found,
     but non-standard types.
     """
+    if not inited:
         init()
     return guess_extension(type, strict)
 
@@ -284,6 +287,7 @@ def add_type(type, ext, strict=True):
     list of standard types, else to the list of non-standard
     types.
     """
+    if not inited:
         init()
     return add_type(type, ext, strict)
 

Misc/NEWS

@@ -166,6 +166,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #5401: Fixed a performance problem in mimetypes when ``from mimetypes
+  import guess_extension`` was used.
+
 - Issue #1733986: Fixed mmap crash in accessing elements of second map object
   with same tagname but larger size than first map. (Windows)