[1.7.x] Fixed #22606 -- Locmemcache has_key() failed for infinite cache expiry

Refactored cache expiry logic for Locmemcache to make consistent across
all places where accessed, and correctly handle None as expiry time.
Backport of 66880e4c from master.

django/core/cache/backends/locmem.py

@@ -29,8 +29,7 @@ class LocMemCache(BaseCache):
         self.validate_key(key)
         pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
         with self._lock.writer():
-            exp = self._expire_info.get(key, 0)
-            if exp is not None and exp <= time.time():
+            if self._has_expired(key):
                 self._set(key, pickled, timeout)
                 return True
             return False
@@ -40,8 +39,7 @@ class LocMemCache(BaseCache):
         self.validate_key(key)
         pickled = None
         with self._lock.reader():
-            exp = self._expire_info.get(key, 0)
-            if exp is None or exp > time.time():
+            if not self._has_expired(key):
                 pickled = self._cache[key]
         if pickled is not None:
             try:
@@ -85,10 +83,7 @@ class LocMemCache(BaseCache):
         key = self.make_key(key, version=version)
         self.validate_key(key)
         with self._lock.reader():
-            exp = self._expire_info.get(key)
-            if exp is None:
-                return False
-            elif exp > time.time():
+            if not self._has_expired(key):
                 return True
 
         with self._lock.writer():
@@ -99,6 +94,12 @@ class LocMemCache(BaseCache):
                 pass
             return False
 
+    def _has_expired(self, key):
+        exp = self._expire_info.get(key, -1)
+        if exp is None or exp > time.time():
+            return False
+        return True
+
     def _cull(self):
         if self._cull_frequency == 0:
             self.clear()

tests/cache/tests.py

@@ -286,6 +286,8 @@ class BaseCacheTests(object):
         cache.set("hello1", "goodbye1")
         self.assertEqual(cache.has_key("hello1"), True)
         self.assertEqual(cache.has_key("goodbye1"), False)
+        cache.set("no_expiry", "here", None)
+        self.assertEqual(cache.has_key("no_expiry"), True)
 
     def test_in(self):
         # The in operator can be used to inspect cache contents