python 反射和内置方法 一、isinstance和issubclass 二、反射 二、内置方法: __str__和__repr__ __del__ item系列 __call__ __len__ __hash__ __eq__
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
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