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Template Method

Template Method en Python

Template Method es un patrón de diseño de comportamiento que te permite definir el esqueleto de un algoritmo en una clase base y permite a las subclases sobrescribir los pasos sin cambiar la estructura general del algoritmo.

Complejidad:

Popularidad:

Ejemplos de uso: El patrón Template Method es muy común en los frameworks Python. Los desarrolladores lo utilizan a menudo para proporcionar a los usuarios de frameworks medios sencillos para extender la funcionalidad estándar utilizando la herencia.

Identificación: El patrón Template Method se puede reconocer por los métodos de comportamiento que ya tienen un comportamiento “por defecto” definido por la clase base.

Ejemplo conceptual

Este ejemplo ilustra la estructura del patrón de diseño Template Method. Se centra en responder las siguientes preguntas:

  • ¿De qué clases se compone?
  • ¿Qué papeles juegan esas clases?
  • ¿De qué forma se relacionan los elementos del patrón?

main.py: Ejemplo conceptual

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) -> None:
        print("AbstractClass says: I am doing the bulk of the work")

    def base_operation2(self) -> None:
        print("AbstractClass says: But I let subclasses override some operations")

    def base_operation3(self) -> None:
        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) -> None:
        pass

    @abstractmethod
    def required_operations2(self) -> None:
        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) -> None:
        pass

    def hook2(self) -> None:
        pass


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) -> None:
        print("ConcreteClass1 says: Implemented Operation1")

    def required_operations2(self) -> None:
        print("ConcreteClass1 says: Implemented Operation2")


class ConcreteClass2(AbstractClass):
    """
    Usually, concrete classes override only a fraction of base class'
    operations.
    """

    def required_operations1(self) -> None:
        print("ConcreteClass2 says: Implemented Operation1")

    def required_operations2(self) -> None:
        print("ConcreteClass2 says: Implemented Operation2")

    def hook1(self) -> None:
        print("ConcreteClass2 says: Overridden Hook1")


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())

Output.txt: Resultado de la ejecución

Same client code can work with different subclasses:
AbstractClass says: I am doing the bulk of the work
ConcreteClass1 says: Implemented Operation1
AbstractClass says: But I let subclasses override some operations
ConcreteClass1 says: Implemented Operation2
AbstractClass says: But I am doing the bulk of the work anyway

Same client code can work with different subclasses:
AbstractClass says: I am doing the bulk of the work
ConcreteClass2 says: Implemented Operation1
AbstractClass says: But I let subclasses override some operations
ConcreteClass2 says: Overridden Hook1
ConcreteClass2 says: Implemented Operation2
AbstractClass says: But I am doing the bulk of the work anyway

Template Method en otros lenguajes

Template Method en C# Template Method en C++ Template Method en Go Template Method en Java Template Method en PHP Template Method en Ruby Template Method en Rust Template Method en Swift Template Method en TypeScript