Fix flyweight_with_metaclass sharing instances for different arguments (#495)

The pool key concatenated str(arg) with no separator, so Card2('1', '0') and
Card2('10') (or Card2(1) and Card2('1')) got the same key and the second call
returned the first call's instance. Use repr of the class name, args and
sorted kwargs instead, which also makes the key independent of kwarg order.
Add tests, since the module had none.

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

Author: Darkslayer3324j

patterns/structural/flyweight_with_metaclass.py

@@ -19,12 +19,11 @@ def __new__(mcs, name, parents, dct):
     def _serialize_params(cls, *args, **kwargs):
         """
         Serialize input parameters to a key.
-        Simple implementation is just to serialize it as a string
+        Simple implementation is just to serialize it as a string. ``repr`` keeps
+        ``("1", "0")``, ``("10",)`` and ``(1,)`` apart, and sorting the keyword
+        arguments makes the key independent of their order.
         """
-        args_list = list(map(str, args))
-        args_list.extend([str(kwargs), cls.__name__])
-        key = "".join(args_list)
-        return key
+        return repr((cls.__name__, args, sorted(kwargs.items())))
 
     def __call__(cls, *args, **kwargs):
         key = FlyweightMeta._serialize_params(cls, *args, **kwargs)

tests/structural/test_flyweight_with_metaclass.py

@@ -0,0 +1,26 @@
+from patterns.structural.flyweight_with_metaclass import Card2
+
+
+def test_same_arguments_share_an_instance():
+    Card2.pool.clear()
+    assert Card2("10", "h", a=1) is Card2("10", "h", a=1)
+
+
+def test_different_arguments_do_not_share_an_instance():
+    Card2.pool.clear()
+    assert Card2("10", "h", a=1) is not Card2("10", "h", a=2)
+
+
+def test_argument_boundaries_are_part_of_the_key():
+    Card2.pool.clear()
+    assert Card2("1", "0") is not Card2("10")
+
+
+def test_argument_types_are_part_of_the_key():
+    Card2.pool.clear()
+    assert Card2(1) is not Card2("1")
+
+
+def test_keyword_argument_order_does_not_matter():
+    Card2.pool.clear()
+    assert Card2(a=1, b=2) is Card2(b=2, a=1)