Also temporarily revert r83871, to fix compilation on buildbots

Doc/library/fnmatch.rst

@@ -84,6 +84,13 @@ patterns.
       <_sre.SRE_Match object at 0x...>
 
 
+.. function:: purge()
+
+   Clear the internal pattern cache.
+
+   .. versionadded:: 3.2
+
+
 .. seealso::
 
    Module :mod:`glob`

Lib/fnmatch.py

@@ -12,9 +12,19 @@ corresponding to PATTERN.  (It does not compile it.)
 import os
 import posixpath
 import re
-import functools
 
-__all__ = ["filter", "fnmatch", "fnmatchcase", "translate"]
+__all__ = ["filter", "fnmatch", "fnmatchcase", "purge", "translate"]
+
+_cache = {}  # Maps text patterns to compiled regexen.
+_cacheb = {}  # Ditto for bytes patterns.
+_MAXCACHE = 100  # Maximum size of caches.
+
+
+def purge():
+    """Clear the pattern cache."""
+    _cache.clear()
+    _cacheb.clear()
+
 
 def fnmatch(name, pat):
     """Test whether FILENAME matches PATTERN.
@@ -35,21 +45,28 @@ def fnmatch(name, pat):
     pat = os.path.normcase(pat)
     return fnmatchcase(name, pat)
 
-@functools.lru_cache(maxsize=250)
-def _compile_pattern(pat, is_bytes=False):
-    if is_bytes:
-        pat_str = str(pat, 'ISO-8859-1')
-        res_str = translate(pat_str)
-        res = bytes(res_str, 'ISO-8859-1')
-    else:
-        res = translate(pat)
-    return re.compile(res).match
+
+def _compile_pattern(pat):
+    cache = _cacheb if isinstance(pat, bytes) else _cache
+    regex = cache.get(pat)
+    if regex is None:
+        if isinstance(pat, bytes):
+            pat_str = str(pat, 'ISO-8859-1')
+            res_str = translate(pat_str)
+            res = bytes(res_str, 'ISO-8859-1')
+        else:
+            res = translate(pat)
+        if len(cache) >= _MAXCACHE:
+            cache.clear()
+        cache[pat] = regex = re.compile(res)
+    return regex.match
+
 
 def filter(names, pat):
     """Return the subset of the list NAMES that match PAT."""
     result = []
     pat = os.path.normcase(pat)
-    match = _compile_pattern(pat, isinstance(pat, bytes))
+    match = _compile_pattern(pat)
     if os.path is posixpath:
         # normcase on posix is NOP. Optimize it away from the loop.
         for name in names:
@@ -61,13 +78,14 @@ def filter(names, pat):
                 result.append(name)
     return result
 
+
 def fnmatchcase(name, pat):
     """Test whether FILENAME matches PATTERN, including case.
 
     This is a version of fnmatch() which doesn't case-normalize
     its arguments.
     """
-    match = _compile_pattern(pat, isinstance(pat, bytes))
+    match = _compile_pattern(pat)
     return match(name) is not None
 
 

Lib/test/test_fnmatch.py

@@ -3,10 +3,15 @@
 from test import support
 import unittest
 
-from fnmatch import fnmatch, fnmatchcase, translate, filter
+from fnmatch import (fnmatch, fnmatchcase, _MAXCACHE, _cache, _cacheb, purge,
+                        translate, filter)
+
 
 class FnmatchTestCase(unittest.TestCase):
 
+    def tearDown(self):
+        purge()
+
     def check_match(self, filename, pattern, should_match=1, fn=fnmatch):
         if should_match:
             self.assertTrue(fn(filename, pattern),
@@ -60,6 +65,22 @@ class FnmatchTestCase(unittest.TestCase):
         self.check_match(b'test\xff', b'te*\xff')
         self.check_match(b'foo\nbar', b'foo*')
 
+    def test_cache_clearing(self):
+        # check that caches do not grow too large
+        # http://bugs.python.org/issue7846
+
+        # string pattern cache
+        for i in range(_MAXCACHE + 1):
+            fnmatch('foo', '?' * i)
+
+        self.assertLessEqual(len(_cache), _MAXCACHE)
+
+        # bytes pattern cache
+        for i in range(_MAXCACHE + 1):
+            fnmatch(b'foo', b'?' * i)
+        self.assertLessEqual(len(_cacheb), _MAXCACHE)
+
+
 class TranslateTestCase(unittest.TestCase):
 
     def test_translate(self):