建造者模式，也是一種創(chuàng)建新對(duì)象的設(shè)計(jì)方法，和C++中的虛函數(shù)很類似，但是用到了python自身的虛基類ABCMeta。

1.應(yīng)用場(chǎng)景:

? ? ?某個(gè)類中的函數(shù)較多，且實(shí)現(xiàn)比較復(fù)雜，很多時(shí)候需要繼承的子類重載或者重新定義邏輯；

2.背景基礎(chǔ)：

? ? 由于用到python中虛函數(shù)，需要了解abc模塊中的ABCMeta和python中類創(chuàng)建對(duì)象時(shí)的__metaclass__屬性含義。

一般地，在某個(gè)類中如果定義__metaclass__=something時(shí)，簡單地說是，創(chuàng)建對(duì)象時(shí)，會(huì)首先找到__metaclass__所指向的對(duì)象something，然后使用該對(duì)象進(jìn)行創(chuàng)建對(duì)象。

3.代碼：

            
              #coding:utf-8

from abc import ABCMeta,abstractmethod


class Builder():
    __metaclass__=ABCMeta

    @abstractmethod
    def draw_head(self):
        pass
    @abstractmethod
    def draw_body(self):
        pass

class Thin(Builder):

    def draw_body(self):
        print("Draw Thin Body")

    def draw_head(self):
        print("Draw Thin Head.")

class Fat(Builder):

    def draw_body(self):
        print("Draw Fat Body")

    def draw_head(self):
        print("Draw fat Head.")


class Director():
    def __init__(self,person):
        self.person = person

    def draw(self):
        self.person.draw_body()
        self.person.draw_head()



if __name__ == "__main__":
    fat=Fat()
    thin=Thin()
    director_thin=Director(thin)
    director_thin.draw()
    director_fat=Director(fat)
    director_fat.draw()

#output:
Draw Thin Body
Draw Thin Head.
Draw Fat Body
Draw fat Head.

            
          

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