python 反射和内置方法

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

class Foo:

    def __init__(self,name,age):
        self.name=name
        self.age=age
    def fun(self):
        print("...........xander")
f=Foo("xander",23)
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'

'''反射'''
class People:
    country = 'china'
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def talk(self):
        print('%s is talking'% self.name)
p = People('xander', 23)
p.talk()
choice = input('>>>:')  # 输入的字符串
print(p.choice)  # p.'name'
 
hasattr(p, 'name')  # 判断p里面有没有p.name,字典中——dict——有没有
hasattr(p, 'talk')
 
print(getattr(p, 'nameqqq', None))  # 取到
print(getattr(p, 'talk', None))
print(getattr(People, 'country'))  # 类也一样
 
setattr(p, 'sex', 'male')  # p.sex = 'male'  修改，新增
print(p.sex)
 
delattr(p, 'age')  # del p.age  删除
print(p.__dict__)

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

'''反射的应用'''
class Service():
    def run(self):
        while 1:
            cd = input('>>>:').strip()  # 根据用户输入执行命令
            cmds = cd.split(' ')
            if hasattr(self, cmds[0]):
                func = getattr(self, cmds[0])
                func(cmds)
    def get(self, cmds):
        print('get......', cmds)
    def put(self, cmds):
        print('put......', cmds)
s = Service()
s.run()

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

'''__str__方法 print()时运行'''
d = dict({'name': 'xander'})
print(isinstance(d, dict))
 
class People:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def __str__(self):
        print('>>>:str')
        return '<name:%s,age:%s>' % (self.name, self.age)
p = People('xander', 23)
print(p)  # p.__str__()

True
>>>:str
<name:xander,age:23>

__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)

'''__del__方法（在对象被删除之前，先运行__del__方法）'''
class Open():
    def __init__(self, filename):
        print('open filename')
        self.filename = filename
    def __del__(self):
        print('填写回收操作系统资源 del......')
a = Open('__init__.py')
del a
a = Open('__init__.py')
print('__main__')  # 程序关闭之前，删除对象之前.__del__方法

open filename
填写回收操作系统资源 del......
open filename
__main__
填写回收操作系统资源 del......

item系列

__getitem__\__setitem__\__delitem__

'''item系列  当成字典来操作'''
class Foo:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def __getitem__(self, item):
        print('getitem...')
        print(self.__dict__[item])
    def __setitem__(self, key, value):
        print('setitem...')
        self.__dict__[key] = value
    def __delitem__(self, key):
        print('delitem...')
        del self.__dict__[key]
f = Foo('xander', 23)
print(f.__dict__)
# 查看属性
f['name']
# 设置属性
f['sex'] = 'boy'
print(f.__dict__)
# 删除属性
del f['sex']
print(f.__dict__)

{'name': 'xander', 'age': 23}
getitem...
xander
setitem...
{'name': 'xander', 'age': 23, 'sex': 'boy'}
delitem...
{'name': 'xander', 'age': 23}

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