day27 反射内置方法

Posted 2020-10-03 A-a

一、isinstance和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))
# 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))

 

二、反射

python面向对象中的反射：通过字符串的形式操作对象相关的属性。python中的一切事物都是对象（都可以使用反射）

四个方法:hasattr(),getattr(),setattr(),delattr()

1.对象中

 

__author__ = ‘ctz‘
class Foo:
    def __init__(self,name,age):
        self.name=name
        self.age=age

    def fun(self):
        print("...........ctz")

f=Foo("ctz",21)
print(hasattr(f,"name"))
print(hasattr(f,"age"))
print(hasattr(f,"fun"))
print(getattr(f,"name"))
print(getattr(f,"age"))
print(getattr(f,"fun"))
fu=getattr(f,"fun")
fu()



print("".center(50,"-"))

setattr(f,"name","egon")
setattr(f,"age",73)

print(f.name,f.age)

print("--------------------")

delattr(f,"name")
print(f.name)

 

True
True
True
ctz
21
<bound method Foo.fun of <__main__.Foo object at 0x00000000023F9DD8>>
...........ctz
--------------------------------------------------
egon 73
--------------------
Traceback (most recent call last):
  File "G:/test/week6/day27/反射1 对象.py", line 32, in <module>
    print(f.name)
AttributeError: ‘Foo‘ object has no attribute ‘name‘

 

 

2.类中

__author__ = ‘Administrator‘
class Foo:
    f=123
    @staticmethod
    def static():
        print("static......")

    @classmethod
    def clas(cls):
        print(cls.f,"class.............")


print(hasattr(Foo,"f"))
print(hasattr(Foo,"static"))
print(hasattr(Foo,"clas"))


if hasattr(Foo,"f"):
    print(getattr(Foo,"f"))

print(getattr(Foo,"static"))
print(getattr(Foo,"clas"))
s=getattr(Foo,"static")
s()
c=getattr(Foo,"clas")
c()

True
True
True
123
<function Foo.static at 0x000000000241B9D8>
<bound method Foo.clas of <class ‘__main__.Foo‘>>
static......
123 class.............

3.模块

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

__author__ = ‘Administrator‘
import aa

print(hasattr(aa,"bb"))
g=getattr(aa,"bb")
g()

def Demo():
    print("本模块自己的反射")

import sys
print(sys.modules)
module=sys.modules[__name__]
if hasattr(module,"Demo"):
    d=getattr(module,"Demo")
    d()

def bb():
    print("bbbbb")
#aa

二、内置方法:

__str__和__repr__

改变对象的字符串显示__str__,__repr__

自定制格式化字符串__format__

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

__del__

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。

__author__ = ‘Administrator‘
class Foo:
    def __del__(self):
        print("执行我来")

f = Foo()
print(123)
print(123)
del f
print(123)
print(123)
print(123)

item系列

__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()
# f[‘name‘] = ‘alex‘
# del f[‘name‘]
# print(f.name)
f1 = Foo()
print(f == f1)
# print(f[0])
# print(f[1])
# print(f[2])

单例模式

class Singleton:
    def __new__(cls, *args, **kw):
        if not hasattr(cls, ‘_instance‘):
            orig = super(Singleton, cls)
            cls._instance = orig.__new__(cls, *args, **kw)
        return cls._instance

one = Singleton()
two = Singleton()

two.a = 3
print(one.a)
# 3
# one和two完全相同,可以用id(), ==, is检测
print(id(one))
# 29097904
print(id(two))
# 29097904
print(one == two)
# True
print(one is two)

单例模式

__call__

对象后面加括号，触发执行。

注：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()()

class Foo:

    def __init__(self):
        pass
    
    def __call__(self, *args, **kwargs):

        print(‘__call__‘)


obj = Foo() # 执行 __init__
obj()       # 执行 __call__

__len__

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

    def __len__(self):
        return len(self.__dict__)
a = A()
print(len(a))

# 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))

__hash__

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

    def __hash__(self):
        return hash(str(self.a)+str(self.b))
a = A()
print(hash(a))

__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)

 

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]

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

纸牌游戏

纸牌游戏2

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

面试题

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 self.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))

一道面试题