Issue 7846: fnmatch cache can grow without bound

Updated to solution to use the functools.lru_cache().
Restores the API so that purge() is not needed
(because the cache never gets big).

Doc/library/fnmatch.rst

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

Lib/fnmatch.py

@@ -12,19 +12,9 @@ corresponding to PATTERN.  (It does not compile it.)
 import os
 import posixpath
 import re
+import functools
 
-__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()
-
+__all__ = ["filter", "fnmatch", "fnmatchcase", "translate"]
 
 def fnmatch(name, pat):
     """Test whether FILENAME matches PATTERN.
@@ -45,28 +35,21 @@ def fnmatch(name, pat):
     pat = os.path.normcase(pat)
     return fnmatchcase(name, pat)
 
-
-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
-
+@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 filter(names, pat):
     """Return the subset of the list NAMES that match PAT."""
     result = []
     pat = os.path.normcase(pat)
-    match = _compile_pattern(pat)
+    match = _compile_pattern(pat, isinstance(pat, bytes))
     if os.path is posixpath:
         # normcase on posix is NOP. Optimize it away from the loop.
         for name in names:
@@ -78,14 +61,13 @@ 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)
+    match = _compile_pattern(pat, isinstance(pat, bytes))
     return match(name) is not None
 
 

Lib/test/test_fnmatch.py

@@ -3,15 +3,10 @@
 from test import support
 import unittest
 
-from fnmatch import (fnmatch, fnmatchcase, _MAXCACHE, _cache, _cacheb, purge,
-                        translate, filter)
-
+from fnmatch import fnmatch, fnmatchcase, 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),
@@ -65,22 +60,6 @@ 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):