Fix #256: Deprecate @mru_cache decorator.

docs/index.rst

@@ -604,6 +604,11 @@ all the decorators in this module are thread-safe by default.
    saves up to `maxsize` results based on a Most Recently Used (MRU)
    algorithm.
 
+   .. deprecated:: 5.4
+
+   The `mru_cache` decorator has been deprecated due to lack of use.
+   Please choose a decorator based on some other algorithm.
+
 .. decorator:: rr_cache(user_function)
                rr_cache(maxsize=128, choice=random.choice, typed=False)
 

src/cachetools/func.py

@@ -82,6 +82,10 @@ def mru_cache(maxsize=128, typed=False):
     up to `maxsize` results based on a Most Recently Used (MRU)
     algorithm.
     """
+    from warnings import warn
+
+    warn("@mru_cache is deprecated", DeprecationWarning, stacklevel=2)
+
     if maxsize is None:
         return _cache({}, None, typed)
     elif callable(maxsize):

tests/test_func.py

@@ -100,30 +100,32 @@ def __eq__(self, other):
 
 
 class FIFODecoratorTest(unittest.TestCase, DecoratorTestMixin):
-
     DECORATOR = staticmethod(cachetools.func.fifo_cache)
 
 
 class LFUDecoratorTest(unittest.TestCase, DecoratorTestMixin):
-
     DECORATOR = staticmethod(cachetools.func.lfu_cache)
 
 
 class LRUDecoratorTest(unittest.TestCase, DecoratorTestMixin):
-
     DECORATOR = staticmethod(cachetools.func.lru_cache)
 
 
 class MRUDecoratorTest(unittest.TestCase, DecoratorTestMixin):
+    def decorator(self, maxsize, **kwargs):
+        import warnings
 
-    DECORATOR = staticmethod(cachetools.func.mru_cache)
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            d = cachetools.func.mru_cache(maxsize, **kwargs)
+        self.assertEqual(len(w), 1)
+        self.assertIs(w[0].category, DeprecationWarning)
+        return d
 
 
 class RRDecoratorTest(unittest.TestCase, DecoratorTestMixin):
-
     DECORATOR = staticmethod(cachetools.func.rr_cache)
 
 
 class TTLDecoratorTest(unittest.TestCase, DecoratorTestMixin):
-
     DECORATOR = staticmethod(cachetools.func.ttl_cache)