Metaclass for caching instances

aloe/parser.py

@@ -41,10 +41,6 @@
 from codecs import open
 from copy import deepcopy
 from collections import OrderedDict
-try:
-    from functools import lru_cache  # pylint:disable=no-name-in-module
-except ImportError:
-    from repoze.lru import lru_cache
 from warnings import warn
 
 import pyparsing
@@ -840,15 +836,6 @@ class Gherkin(object):
     Gherkin parser
     """
 
-    @classmethod
-    @lru_cache(20)
-    def get_parser(cls, language):
-        """
-        Get a parser for a specific language.
-        """
-
-        return cls(language=language)
-
     def __init__(self, language):
         self.language = language
 
@@ -1017,7 +1004,7 @@ def parse(string=None,
     if not language:
         language = guess_language(string, filename)
 
-    parser = parser_class.get_parser(language)
+    parser = parser_class(language)
 
     #
     # Try parsing the string

aloe/utils.py

@@ -28,6 +28,10 @@
 import re
 import sys
 
+try:
+    from functools import lru_cache  # pylint:disable=no-name-in-module
+except ImportError:
+    from repoze.lru import lru_cache
 from contextlib import contextmanager
 
 
@@ -98,3 +102,14 @@ def __get__(self, instance, owner):
         result = self.func(instance)
         instance.__dict__[self.name] = result
         return result
+
+
+class memoizedtype(type):  # pylint:disable=invalid-name
+    """
+    A type that caches the created instances.
+    """
+
+    @lru_cache(20)
+    def __call__(cls, *args, **kwargs):
+        # On Python 2, newsuper can't deal with metaclasses
+        return super(memoizedtype, cls).__call__(*args, **kwargs)

tests/unit/test_utils.py

@@ -24,6 +24,7 @@
 from __future__ import absolute_import
 from future import standard_library
 standard_library.install_aliases()
+from future.utils import with_metaclass
 
 import sys
 import unittest
@@ -34,6 +35,7 @@
 from aloe.utils import (
     unwrap_function,
     memoizedproperty,
+    memoizedtype,
 )
 
 
@@ -109,3 +111,35 @@ def prop(self):
         # Test that different objects aren't sharing the value
         self.assertEqual(second.prop, 11)
         self.assertEqual(second.prop, 11)
+
+    def test_memoizedtype(self):
+        """Test memoizedtype."""
+
+        class Memoized(with_metaclass(memoizedtype, object)):
+            """A class to test memoizedtype."""
+
+            counter = 0
+
+            def __init__(self, value):
+                """
+                A constructor that intentionally modifies the class state.
+                """
+
+                self.value = value
+                type(self).counter += 1
+
+        first = Memoized(5)
+        second = Memoized(10)
+
+        # Check the objects are created properly
+        self.assertEqual(first.value, 5)
+        self.assertEqual(second.value, 10)
+
+        # Try to create the same object again
+        another_first = Memoized(5)
+
+        # It should be the same as before
+        self.assertIs(first, another_first)
+
+        # Only two objects should have been created
+        self.assertEqual(Memoized.counter, 2)