add code example

behavioral/template/abstract_class.py

@@ -0,0 +1,57 @@
+from abc import ABC, abstractmethod
+
+
+class AbstractClass(ABC):
+    """
+    The Abstract Class defines a template method that contains a skeleton of
+    some algorithm, composed of calls to (usually) abstract primitive
+    operations.
+
+    Concrete subclasses should implement these operations, but leave the
+    template method itself intact.
+    """
+
+    def template_method(self) -> None:
+        """
+        The template method defines the skeleton of an algorithm.
+        """
+
+        self.base_operation1()
+        self.required_operations1()
+        self.base_operation2()
+        self.hook1()
+        self.required_operations2()
+        self.base_operation3()
+        self.hook2()
+
+    """These operations already have implementations."""
+
+    def base_operation1(self):
+        print("AbstractClass says: I am doing the bulk of the work")
+
+    def base_operation2(self):
+        print("AbstractClass says: But I let subclasses override some operations")
+
+    def base_operation3(self):
+        print("AbstractClass says: But I am doing the bulk of the work anyway")
+
+    """These operations have to be implemented in subclasses."""
+
+    @abstractmethod
+    def required_operations1(self):
+        pass
+
+    @abstractmethod
+    def required_operations2(self):
+        pass
+
+    """
+    These are "hooks." Subclasses may override them, but it's not mandatory since the hooks already have default (but
+    empty) implementation. Hooks provide additional extension points in some crucial places of the algorithm.
+    """
+
+    def hook1(self):
+        pass
+
+    def hook2(self):
+        pass

behavioral/template/concrete_classes.py

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+from behavioral.template.abstract_class import AbstractClass
+
+
+class ConcreteClass1(AbstractClass):
+    """
+    Concrete classes have to implement all abstract operations of the base
+    class. They can also override some operations with a default implementation.
+    """
+
+    def required_operations1(self):
+        print("ConcreteClass1 says: Implemented Operation1")
+
+    def required_operations2(self):
+        print("ConcreteClass1 says: Implemented Operation2")
+
+
+class ConcreteClass2(AbstractClass):
+    """
+    Usually, concrete classes override only a fraction of base class' operations.
+    """
+
+    def required_operations1(self):
+        print("ConcreteClass2 says: Implemented Operation1")
+
+    def required_operations2(self):
+        print("ConcreteClass2 says: Implemented Operation2")
+
+    def hook1(self):
+        print("ConcreteCLass2 says: Overridden Hook1")

behavioral/template/main.py

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+from behavioral.template.abstract_class import AbstractClass
+from behavioral.template.concrete_classes import ConcreteClass1, ConcreteClass2
+
+
+def client_code(abstract_class: AbstractClass) -> None:
+    """
+    The client code calls the template method to execute the algorithm. Client
+    code does not have to know the concrete class of an object it works with, as
+    long as it works with objects through the interface of their base class.
+    """
+
+    abstract_class.template_method()
+
+
+if __name__ == "__main__":
+    print("Same client code can work with different subclasses:")
+    client_code(ConcreteClass1())
+    print("")
+
+    print("Same client code can work with different subclasses:")
+    client_code(ConcreteClass2())