implemented chain of responsibility pattern.

pypatterns/behavioral/chain.py

@@ -0,0 +1,79 @@
+from abc import ABCMeta, abstractmethod
+
+
+class ChainException(Exception):
+    """
+    Exception for when a chain link could not handle a request.
+    """
+    pass
+
+
+class ChainLink(object, metaclass=ABCMeta):
+    """
+    Abstract ChainLink object as part of the Chain of Responsibility pattern.
+    """
+    def __init__(self):
+        """
+        Initialize a new ChainLink instance.
+        """
+        self.successor = None
+
+    def set_successor(self, successor):
+        """
+        Set a chain link to call if this chain link fails.
+
+        @param successor: The chain link to call if this chain link fails.
+        @type successor: ChainLink
+        """
+        self.successor = successor
+
+    def successor_handle(self, request):
+        """
+        Have this chain links successor handle a request.
+
+        @param request: The request to handle.
+        """
+        try:
+            return self.successor.handle(request)
+        except AttributeError:
+            raise ChainException
+
+    @abstractmethod
+    def handle(self, request):
+        """
+        Handle a request.
+
+        @param request: The request to handle.
+        """
+        pass
+
+
+class Chain(object, metaclass=ABCMeta):
+    """
+    Abstract Chain class as part of the Chain of Responsibility pattern.
+    """
+    def __init__(self, chainlink):
+        """
+        Initialize a new Chain instance.
+
+        @param chainlink: The starting chain link.
+        """
+        self.chainlink = chainlink
+
+    def handle(self, request):
+        """
+        Handle a request.
+
+        @param request: The request to handle.
+        """
+        try:
+            return self.chainlink.handle(request)
+        except ChainException:
+            return self.fail()
+
+    @abstractmethod
+    def fail(self):
+        """
+        The method to call when the chain could not handle a request.
+        """
+        pass

setup.py

@@ -6,7 +6,9 @@ setup(
     description='Python Design Patterns',
     author='Tyler LaBerge',
     packages=[
-          'pypatterns',
+        'pypatterns',
-          'pypatterns.creational'
+        'pypatterns.creational',
+        'pypatterns.behavioral'
     ],
 )
+

tests/behavioral_tests/test_chain.py

@@ -0,0 +1,140 @@
+from unittest import TestCase
+from pypatterns.behavioral.chain import ChainException, ChainLink, Chain
+
+
+class ChainLinkTestCase(TestCase):
+    """
+    Unit testing class for the ChainLink class.
+    """
+    def setUp(self):
+        """
+        Initialize testing data.
+        """
+        class ConcreteChainLinkThree(ChainLink):
+
+            def handle(self, request):
+                if request == 'handle_three':
+                    return "Handled in chain link three"
+                else:
+                    return self.successor_handle(request)
+
+        class ConcreteChainLinkTwo(ChainLink):
+
+            def __init__(self):
+                super().__init__()
+                self.set_successor(ConcreteChainLinkThree())
+
+            def handle(self, request):
+                if request == 'handle_two':
+                    return "Handled in chain link two"
+                else:
+                    return self.successor_handle(request)
+
+        class ConcreteChainLinkOne(ChainLink):
+
+            def __init__(self):
+                super().__init__()
+                self.set_successor(ConcreteChainLinkTwo())
+
+            def handle(self, request):
+                if request == 'handle_one':
+                    return "Handled in chain link one"
+                else:
+                    return self.successor_handle(request)
+
+        self.chain_link_one_class = ConcreteChainLinkOne
+
+    def test_success_handle(self):
+        """
+        Test the handle method with successful requests.
+
+        @raise AssertionError: If the test fails.
+        """
+        handler = self.chain_link_one_class()
+
+        self.assertEquals("Handled in chain link one", handler.handle("handle_one"))
+        self.assertEquals("Handled in chain link two", handler.handle("handle_two"))
+        self.assertEquals("Handled in chain link three", handler.handle("handle_three"))
+
+    def test_fail_handle(self):
+        """
+        Test the handle method with unsuccessful requests.
+
+        @raise AssertionError: If the test fails.
+        """
+        handler = self.chain_link_one_class()
+        with self.assertRaises(ChainException):
+            handler.handle("foo")
+
+
+class ChainTestCase(TestCase):
+    """
+    Unit testing class for the Chain class.
+    """
+    def setUp(self):
+        """
+        Initialize testing data.
+        """
+        class ConcreteChainLinkThree(ChainLink):
+
+            def handle(self, request):
+                if request == 'handle_three':
+                    return "Handled in chain link three"
+                else:
+                    return self.successor_handle(request)
+
+        class ConcreteChainLinkTwo(ChainLink):
+
+            def __init__(self):
+                super().__init__()
+                self.set_successor(ConcreteChainLinkThree())
+
+            def handle(self, request):
+                if request == 'handle_two':
+                    return "Handled in chain link two"
+                else:
+                    return self.successor_handle(request)
+
+        class ConcreteChainLinkOne(ChainLink):
+
+            def __init__(self):
+                super().__init__()
+                self.set_successor(ConcreteChainLinkTwo())
+
+            def handle(self, request):
+                if request == 'handle_one':
+                    return "Handled in chain link one"
+                else:
+                    return self.successor_handle(request)
+
+        class ConcreteChain(Chain):
+
+            def __init__(self):
+                super().__init__(ConcreteChainLinkOne())
+
+            def fail(self):
+                return 'Fail'
+
+        self.chain_class = ConcreteChain
+
+    def test_success_handle(self):
+        """
+        Test the handle method with a successful request
+
+        @raise AssertionError: If the test fails.
+        """
+        chain = self.chain_class()
+
+        self.assertEquals("Handled in chain link one", chain.handle("handle_one"))
+        self.assertEquals("Handled in chain link two", chain.handle("handle_two"))
+        self.assertEquals("Handled in chain link three", chain.handle("handle_three"))
+
+    def test_fail_handle(self):
+        """
+        Test the handle method with unsuccessful requests.
+
+        @raise AssertionError: If the test fails.
+        """
+        chain = self.chain_class()
+
+        self.assertEquals("Fail", chain.handle("foo"))