Implemented Visitor pattern

pypatterns/behavioral/visitor.py

@@ -0,0 +1,50 @@
+from abc import ABCMeta, abstractmethod
+
+
+class Visitor(metaclass=ABCMeta):
+    """
+    Abstract Visitor class as part of the Visitor Design Pattern.
+    """
+    def visit(self, node, *args, **kwargs):
+        """
+        Visit the visitor with some object.
+
+        @param node: An object to call a visitor method with.
+        @param args: Arguments to go with the visitor method call.
+        @param kwargs: Keyword arguments to go with the visitor method call.
+        @return: The return value of the method that was called for visiting object.
+        """
+        method = None
+        for cls in node.__class__.__mro__:
+            method_name = 'visit_'+cls.__name__.lower()
+            method = getattr(self, method_name, None)
+            if method:
+                break
+
+        if not method:
+            method = self.generic_visit
+        return method(node, *args, **kwargs)
+
+    @abstractmethod
+    def generic_visit(self, node, *args, **kwargs):
+        """
+        The method to call if no methods were found for a visiting object.
+
+        @param node: An object to call a visitor method with.
+        @param args: Arguments to go with the visitor method call.
+        @param kwargs: Keyword arguments to go with the visitor method call.
+        """
+
+
+class Visitee(object):
+    """
+    A base class for objects that wish to be able to visit a Visitor class.
+    """
+    def accept(self, visitor):
+        """
+        Visit a visitor with this class instance.
+
+        @param visitor: The visitor to visit.
+        @type visitor: Visitor
+        """
+        return visitor.visit(self)

tests/behavioral_tests/test_visitor.py

@@ -0,0 +1,104 @@
+from unittest import TestCase
+from pypatterns.behavioral.visitor import Visitor, Visitee
+
+
+class VisitorTestCase(TestCase):
+    """
+    Unit testing class for the Visitor class.
+    """
+    def setUp(self):
+        """
+        Initialize testing data.
+        """
+        class Node(object):
+            pass
+
+        class A(Node):
+            pass
+
+        class B(Node):
+            pass
+
+        class C(A, B):
+            pass
+
+        class NodeVisitor(Visitor):
+
+            def generic_visit(self, node, *args, **kwargs):
+                return 'generic_visit ' + node.__class__.__name__
+
+            def visit_b(self, node, *args, **kwargs):
+                return 'visit_b ' + node.__class__.__name__
+
+        self.a = A()
+        self.b = B()
+        self.c = C()
+        self.node_visitor = NodeVisitor()
+
+    def test_generic_visit(self):
+        """
+        Test that the generic_visit method is called.
+
+        @raise AssertionError: If the test fails.
+        """
+        self.assertEquals('generic_visit A', self.node_visitor.visit(self.a))
+
+    def test_non_generic_visit(self):
+        """
+        Test that a non_generic visit method is called.
+
+        @raise AssertionError: If the test fails.
+        """
+        self.assertEquals('visit_b B', self.node_visitor.visit(self.b))
+
+    def test_inheritance_visit(self):
+        """
+        Test that a parent visit method is called if a child does not have one.
+
+        @raise AssertionError: If the test fails.
+        """
+        self.assertEquals('visit_b C', self.node_visitor.visit(self.c))
+
+
+class VisiteeTestCase(TestCase):
+    """
+    Unit testing class for the Visitee class.
+    """
+    def setUp(self):
+        """
+        Initialize testing data.
+        """
+
+        class Node(object):
+            pass
+
+        class A(Node, Visitee):
+            pass
+
+        class B(A, Visitee):
+            pass
+
+        class C(B, Visitee):
+            pass
+
+        class NodeVisitor(Visitor):
+            def generic_visit(self, node, *args, **kwargs):
+                return 'generic_visit ' + node.__class__.__name__
+
+            def visit_b(self, node, *args, **kwargs):
+                return 'visit_b ' + node.__class__.__name__
+
+        self.a = A()
+        self.b = B()
+        self.c = C()
+        self.visitor = NodeVisitor()
+
+    def test_accept(self):
+        """
+        Test the accept method.
+
+        @raise AssertionError: If the test fails.
+        """
+        self.assertEquals('generic_visit A', self.a.accept(self.visitor))
+        self.assertEquals('visit_b B', self.b.accept(self.visitor))
+        self.assertEquals('visit_b C', self.c.accept(self.visitor))