编程思想设计模式创建模式creational建造者模式builder

Posted 2020-11-04 炼狱腾蛇

Python版

https://github.com/faif/python-patterns/blob/master/creational/builder.py

 

#!/usr/bin/python
# -*- coding : utf-8 -*-

"""
*What is this pattern about?
It decouples the creation of a complex object and its representation,
so that the same process can be reused to build objects from the same
family.
>>他降低了创建复杂类的难度和重现他的难度，因此相同的流程在相同家族总可以被重用
This is useful when you must separate the specification of an object
from its actual representation (generally for abstraction).
>>当你必须把它特殊的部分从他实际的表现中分离出来的时候很有用，通常用来做抽象

*What does this example do?

The first example achieves this by using an abstract base
class for a building, where the initializer (__init__ method) specifies the
steps needed, and the concrete subclasses implement these steps.
>>第一个例子达到了这个目的，他使用一个抽象的积累构建了一个building，
>>初始化方法（__init__）指定了需要的方法，这个实际的子类实现了这些步骤

In other programming languages, a more complex arrangement is sometimes
necessary. In particular, you cannot have polymorphic behaviour in a
constructor in C++ - see https://stackoverflow.com/questions/1453131/how-can-i-get-polymorphic-behavior-in-a-c-constructor
>>在其他的开发语言中，往往需要更加复杂的设计。就像在C++中不能使用多态一样
- which means this Python technique will not work. The polymorphism
required has to be provided by an external, already constructed
instance of a different class.
>>这就意味着python技术不好使了。多态需要外部的，已经构成的，不同的类型的实例来支持

In general, in Python this won‘t be necessary, but a second example showing
this kind of arrangement is also included.
>>总的来说，在python中，这个不是必须的，但是第二个例子表明这种设计也是可以的

*Where is the pattern used practically?

*References:
https://sourcemaking.com/design_patterns/builder

*TL;DR80
Decouples the creation of a complex object and its representation.
"""


# Abstract Building
class Building(object):

    def __init__(self):
        self.build_floor()
        self.build_size()

    def build_floor(self):
        raise NotImplementedError

    def build_size(self):
        raise NotImplementedError

    def __repr__(self):
        return ‘Floor: {0.floor} | Size: {0.size}‘.format(self)


# Concrete Buildings
class House(Building):

    def build_floor(self):
        self.floor = ‘One‘

    def build_size(self):
        self.size = ‘Big‘


class Flat(Building):

    def build_floor(self):
        self.floor = ‘More than One‘

    def build_size(self):
        self.size = ‘Small‘


# In some very complex cases, it might be desirable to pull out the building
# logic into another function (or a method on another class), rather than being
# in the base class ‘__init__‘. (This leaves you in the strange situation where
# a concrete class does not have a useful constructor)


class ComplexBuilding(object):
    def __repr__(self):
        return ‘Floor: {0.floor} | Size: {0.size}‘.format(self)


class ComplexHouse(ComplexBuilding):
    def build_floor(self):
        self.floor = ‘One‘

    def build_size(self):
        self.size = ‘Big and fancy‘


def construct_building(cls):
    building = cls()
    building.build_floor()
    building.build_size()
    return building


# Client
if __name__ == "__main__":
    house = House()
    print(house)
    flat = Flat()
    print(flat)

    # Using an external constructor function:
    complex_house = construct_building(ComplexHouse)
    print(complex_house)

### OUTPUT ###
# Floor: One | Size: Big
# Floor: More than One | Size: Small
# Floor: One | Size: Big and fancy

Python转载版