Implemented Flyweight design pattern.

pypatterns/structural/flyweight.py

@@ -0,0 +1,43 @@
+class FlyweightMeta(type):
+    """
+    Flyweight meta class as part of the Flyweight design pattern.
+    """
+    def __new__(mcs, name, bases, attrs):
+        """
+        Override class construction to add 'pool' attribute to classes dict.
+        @param name: The name of the class.
+        @param bases: Base classes of the class.
+        @param attrs: Attributes of the class.
+        @return: A new Class.
+        """
+        attrs['pool'] = dict()
+        return super(FlyweightMeta, mcs).__new__(mcs, name, bases, attrs)
+
+    @staticmethod
+    def _serialize_params(cls, *args, **kwargs):
+        """
+        Serialize input parameters to a key.
+        Simple implementation is just to serialize it as a string
+        """
+        args_list = [str(arg) for arg in args]
+        args_list.extend([str(kwargs), cls.__name__])
+        key = ''.join(args_list)
+        return key
+
+    def __call__(cls, *args, **kwargs):
+        """
+        Override call to use objects from a pool if identical parameters are used for object creation.
+
+        @param args: Arguments for class instantiation.
+        @param kwargs: Keyword arguments for class instantiation.
+        @return: A new instance of the class.
+        """
+        key = FlyweightMeta._serialize_params(cls, *args, **kwargs)
+        pool = getattr(cls, 'pool', {})
+
+        instance = pool.get(key)
+        if not instance:
+            instance = super(FlyweightMeta, cls).__call__(*args, **kwargs)
+            pool[key] = instance
+
+        return instance

tests/structural_tests/test_flyweight.py

@@ -0,0 +1,32 @@
+from unittest import TestCase
+from pypatterns.structural.flyweight import FlyweightMeta
+
+
+class FlyweightMetaTestCase(TestCase):
+    """
+    Unit testing class for the FlyweightMeta class.
+    """
+    def setUp(self):
+        """
+        Initialize testing data.
+        """
+        class Card(object, metaclass=FlyweightMeta):
+
+            def __init__(self, suit, value):
+                self.suit = suit
+                self.value = value
+
+        self.card_class = Card
+
+    def test_flyweight(self):
+        """
+        Test that new objects with the same params are actually equal.
+
+        @raise AssertionError: If the test fails.
+        """
+        three_of_spades = self.card_class('Spade', 3)
+        four_of_spades = self.card_class('Spade', 4)
+        three_of_spades_two = self.card_class('Spade', 3)
+
+        self.assertEqual(id(three_of_spades), id(three_of_spades_two))
+        self.assertNotEqual(id(three_of_spades), id(four_of_spades))