Python object-oriented advanced chapter

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I learned the three major features of object-oriented inheritance, polymorphism, and encapsulation. Today we look at some advanced content of object-oriented, reflection and some built-in functions of classes.

1. isinstance and issubclass

##

class Foo:
 pass

class Son(Foo):
 pass

s = Son()
#判断一个对象是不是这个类的对象,传两个参数（对象，类）
print(isinstance(s,Son))
print(isinstance(s,Foo))
#type更精准
print(type(s) is Son)
print(type(s) is Foo)

#判断一个类是不是另一类的子类，传两个参数(子类，父类)
print(issubclass(Son,Foo))
print(issubclass(Son,object))
print(issubclass(Foo,object))
print(issubclass(int,object))

2. Reflection

The concept of reflection was first proposed by Smith in 1982. It mainly refers to the ability of a program to access, detect and modify its own state or behavior (introspection). The introduction of this concept quickly triggered research on applied reflectivity in the field of computer science. It was first adopted in the field of programming language design, and has achieved results in Lisp and object-oriented.

Reflection in python object-oriented: Manipulate object-related attributes in the form of strings. Everything in python is an object (reflection can be used)

Four functions that can implement reflection: hasattr, getattr, setattr, delattr

The following methods are applicable Regarding classes and objects (everything is an object, the class itself is also an object)

class Foo:
 def __init__(self):
  self.name = 'egon'
  self.age = 73

 def func(self):
  print(123)

egg = Foo()
#常用：
#hasattr
#getattr
# print(hasattr(egg,'name'))
print(getattr(egg,'name'))
if hasattr(egg,'func'): #返回bool
 Foo_func = getattr(egg,'func') #如果存在这个方法或者属性，就返回属性值或者方法的内存地址
         #如果不存在，报错，因此要配合hasattr使用
 Foo_func()
#不常用：
#setattr
# setattr(egg,'sex','属性值')
# print(egg.sex)
# def show_name(self):
#  print(self.name + ' sb')
# setattr(egg,'sh_name',show_name)
# egg.sh_name(egg)
# show_name(egg)
# egg.sh_name()

#delattr
# delattr(egg,'name')
# print(egg.name)


# print(egg.name)
# egg.func()
# print(egg.__dict__)


#反射
#可以用字符串的方式去访问对象的属性、调用对象的方法
反射举例1

class Foo:
 f = 123 #类变量
 @classmethod
 def class_method_demo(cls):
  print('class_method_demo')
 @staticmethod
 def static_method_demo():
  print('static_method_demo')
# if hasattr(Foo,'f'):
#  print(getattr(Foo,'f'))
print(hasattr(Foo,'class_method_demo'))
method = getattr(Foo,'class_method_demo')
method()
print(hasattr(Foo,'static_method_demo'))
method2 = getattr(Foo,'static_method_demo')
method2()
#类也是对象

Reflection example 2

import my_module
# print(hasattr(my_module,'test'))
# # func_test = getattr(my_module,'test')
# # func_test()
# getattr(my_module,'test')()
#import其他模块应用反射

from my_module import test


def demo1():
 print('demo1')

import sys
print(__name__) #'__main__'
print(sys.modules)
#&#39;__main__&#39;: <module &#39;__main__&#39; from &#39;D:/Python代码文件存放目录/S6/day26/6反射3.py&#39;>
module_obj =sys.modules[__name__] #sys.modules[&#39;__main__&#39;]
# module_obj : <module &#39;__main__&#39; from &#39;D:/Python代码文件存放目录/S6/day26/6反射3.py&#39;>
print(module_obj)
print(hasattr(module_obj,&#39;demo1&#39;))
getattr(module_obj,&#39;demo1&#39;)()
#在本模块中应用反射
反射举例3

#对象
#类
#模块 ： 本模块和导入的模块

def register():
 print('register')

def login():
 pass

def show_shoppinglst():
 pass
#
print('注册，登录')
ret = input('欢迎，请输入您要做的操作： ')
import sys
print(sys.modules)
# my_module = sys.modules[__name__]
# if hasattr(my_module,ret):
#  getattr(my_module,ret)()
if ret == '注册':
 register()
elif ret == '登录':
 login()
elif ret == 'shopping':
 show_shoppinglst()
反射举例4

def test():
 print('test')

3. Class built-in functions

1, __str__ and __repr__

class Foo:
 def __init__(self,name):
  self.name = name
 def __str__(self):
  return '%s obj info in str'%self.name
 def __repr__(self):
  return 'obj info in repr'

f = Foo('egon')
# print(f)
print('%s'%f)
print('%r'%f)
print(repr(f)) # f.__repr__()
print(str(f))
#当打印一个对象的时候，如果实现了str，打印中的返回值
#当str没有被实现的时候，就会调用repr方法
#但是当你用字符串格式化的时候 %s和%r会分别去调用__str__和__repr__
#不管是在字符串格式化的时候还是在打印对象的时候，repr方法都可以作为str方法的替补
#但反之不行
#用于友好的表示对象。如果str和repr方法你只能实现一个：先实现repr

2, __del__

class Foo:
 def __del__(self):
  print('执行我啦')

f = Foo()
print(123)
print(123)
print(123)
#析构方法，当对象在内存中被释放时，自动触发执行。
#注：此方法一般无须定义，因为Python是一门高级语言，程序员在使用时无需关心内存的分配和释放，因为此工作都是交给Python解释器来执行，所以，析构函数的调用是由解释器在进行垃圾回收时自动触发执行的。

3. item series

__getitem__\__setitem__\__delitem__

class Foo:
 def __init__(self):
  self.name = 'egon'
  self.age = 73
  
 def __getitem__(self, item):
  return self.__dict__[item]

 def __setitem__(self, key, value):
  # print(key,value)
  self.__dict__[key] = value

 def __delitem__(self, key):
  del self.__dict__[key]
f = Foo()
print(f['name'])
print(f['age'])
f['name'] = 'alex'
# del f['name']
print(f.name)
f1 = Foo()
print(f == f1)

4, __new__

# class A:
#  def __init__(self): #有一个方法在帮你创造self
#   print('in init function')
#   self.x = 1
#
#  def __new__(cls, *args, **kwargs):
#   print('in new function')
#   return object.__new__(A, *args, **kwargs)
# a = A()
# b = A()
# c = A()
# d = A()
# print(a,b,c,d)

#单例模式
class Singleton:
 def __new__(cls, *args, **kw):
  if not hasattr(cls, '_instance'):
   cls._instance = object.__new__(cls, *args, **kw)
  return cls._instance

one = Singleton()
two = Singleton()
three = Singleton()
go = Singleton()
print(one,two)

one.name = 'alex'
print(two.name)

5, __call__

class Foo:
 def __init__(self):
  pass
 def __call__(self, *args, **kwargs):
  print('__call__')

obj = Foo() # 执行 __init__
obj() # 执行 __call__
Foo()() # 执行 __init__和执行 __call__
#构造方法的执行是由创建对象触发的，即：对象 = 类名() ；而对于 __call__ 方法的执行是由对象后加括号触发的，即：对象() 或者 类()()

6, __len__, __hash__

class Foo:
 def __len__(self):
  return len(self.__dict__)
 def __hash__(self):
  print('my hash func')
  return hash(self.name)
f = Foo()
print(len(f))
f.name = 'egon'
print(len(f))
print(hash(f))

7, __eq__

class A:
 def __init__(self):
  self.a = 1
  self.b = 2

 def __eq__(self,obj):
  if self.a == obj.a and self.b == obj.b:
   return True
a = A()
b = A()
print(a == b)

#__eq__控制着==的结果

8. Built-in function examples

class FranchDeck:
 ranks = [str(n) for n in range(2,11)] + list('JQKA')
 suits = ['红心','方板','梅花','黑桃']

 def __init__(self):
  self._cards = [Card(rank,suit) for rank in FranchDeck.ranks
          for suit in FranchDeck.suits]

 def __len__(self):
  return len(self._cards)

 def __getitem__(self, item):
  return self._cards[item]

deck = FranchDeck()
print(deck[0])
from random import choice
print(choice(deck))
print(choice(deck))

纸牌游戏

class FranchDeck:
 ranks = [str(n) for n in range(2,11)] + list('JQKA')
 suits = ['红心','方板','梅花','黑桃']

 def __init__(self):
  self._cards = [Card(rank,suit) for rank in FranchDeck.ranks
          for suit in FranchDeck.suits]

 def __len__(self):
  return len(self._cards)

 def __getitem__(self, item):
  return self._cards[item]

 def __setitem__(self, key, value):
  self._cards[key] = value

deck = FranchDeck()
print(deck[0])
from random import choice
print(choice(deck))
print(choice(deck))

from random import shuffle
shuffle(deck)
print(deck[:5])

纸牌游戏2

class Person:
 def __init__(self,name,age,sex):
  self.name = name
  self.age = age
  self.sex = sex

 def __hash__(self):
  return hash(self.name+self.sex)

 def __eq__(self, other):
  if self.name == other.name and other.sex == other.sex:return True


p_lst = []
for i in range(84):
 p_lst.append(Person('egon',i,'male'))

print(p_lst)
print(set(p_lst))

#只要姓名和年龄相同就默认为一人去重

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