Python 模板方法模式讲解和代码示例
模版方法是一种行为设计模式， 它在基类中定义了一个算法的框架， 允许子类在不修改结构的情况下重写算法的特定步骤。
复杂度：
流行度：
使用示例： 模版方法模式在 Python 框架中很常见。 开发者通常使用它来向框架用户提供通过继承实现的、 对标准功能进行扩展的简单方式。
识别方法： 模版方法可以通过行为方法来识别， 该方法已有一个在基类中定义的 “默认” 行为。
概念示例
本例说明了模板方法设计模式的结构并重点回答了下面的问题：
- 它由哪些类组成？
- 这些类扮演了哪些角色？
- 模式中的各个元素会以何种方式相互关联？
main.py: 概念示例
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: 执行结果
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
