isinstance和issubclass
isinstance(obj,cls)检查是否obj是否是类 cls 的对象
class Foo(object):
pass
obj = Foo()
isinstance(obj, Foo)
issubclass(sub, super)检查sub类是否是 super 类的派生类
class Foo(object):
pass
class Bar(Foo):
pass
issubclass(Bar, Foo)
反射
1 什么是反射
反射的概念是由Smith在1982年首次提出的，主要是指程序可以访问、检测和修改它本身状态或行为的一种能力（自省）。这一概念的提出很快引发了计算机科学领域关于应用反射性的研究。它首先被程序语言的设计领域所采用,并在Lisp和面向对象方面取得了成绩。
2 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）
四个可以实现自省的函数
下列方法适用于类和对象（一切皆对象，类本身也是一个对象）
def hasattr(*args, **kwargs): # real signature unknown """ Return whether the object has an attribute with the given name. This is done by calling getattr(obj, name) and catching AttributeError. """ pass
def getattr(object, name, default=None): # known special case of getattr """ getattr(object, name[, default]) -> value Get a named attribute from an object; getattr(x, 'y') is equivalent to x.y. When a default argument is given, it is returned when the attribute doesn't exist; without it, an exception is raised in that case. """ pass
def setattr(x, y, v): # real signature unknown; restored from __doc__ """ Sets the named attribute on the given object to the specified value. setattr(x, 'y', v) is equivalent to ``x.y = v'' """ pass
def delattr(x, y): # real signature unknown; restored from __doc__ """ Deletes the named attribute from the given object. delattr(x, 'y') is equivalent to ``del x.y'' """ pass
class Foo: f = '类的静态变量' def __init__(self,name,age): self.name=name self.age=age def say_hi(self): print('hi,%s'%self.name) obj=Foo('egon',73) #检测是否含有某属性 print(hasattr(obj,'name')) print(hasattr(obj,'say_hi')) #获取属性 n=getattr(obj,'name') print(n) func=getattr(obj,'say_hi') func() print(getattr(obj,'aaaaaaaa','不存在啊')) #报错 #设置属性 setattr(obj,'sb',True) setattr(obj,'show_name',lambda self:self.name+'sb') print(obj.__dict__) print(obj.show_name(obj)) #删除属性 delattr(obj,'age') delattr(obj,'show_name') delattr(obj,'show_name111')#不存在,则报错 print(obj.__dict__)
class Foo(object): staticField = "old boy" def __init__(self): self.name = 'wupeiqi' def func(self): return 'func' @staticmethod def bar(): return 'bar' print getattr(Foo, 'staticField') print getattr(Foo, 'func') print getattr(Foo, 'bar')
import sys def s1(): print ('s1') def s2(): print( 's2') this_module = sys.modules[__name__] hasattr(this_module, 's1') getattr(this_module, 's2')
导入其他模块，利用反射查找该模块是否存在某个方法
#!/usr/bin/env python # -*- coding:utf-8 -*- def test(): print('from the test')
#!/usr/bin/env python # -*- coding:utf-8 -*- """ 程序目录： module_test.py index.py 当前文件： index.py """ import module_test as obj #obj.test() print(hasattr(obj,'test')) getattr(obj,'test')()
__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__
#_*_coding:utf-8_*_ format_dict={ 'nat':'{obj.name}-{obj.addr}-{obj.type}',#学校名-学校地址-学校类型 'tna':'{obj.type}:{obj.name}:{obj.addr}',#学校类型:学校名:学校地址 'tan':'{obj.type}/{obj.addr}/{obj.name}',#学校类型/学校地址/学校名 } class School: def __init__(self,name,addr,type): self.name=name self.addr=addr self.type=type def __repr__(self): return 'School(%s,%s)' %(self.name,self.addr) def __str__(self): return '(%s,%s)' %(self.name,self.addr) def __format__(self, format_spec): # if format_spec if not format_spec or format_spec not in format_dict: format_spec='nat' fmt=format_dict[format_spec] return fmt.format(obj=self) s1=School('oldboy1','北京','私立') print('from repr: ',repr(s1)) print('from str: ',str(s1)) print(s1) ''' str函数或者print函数--->obj.__str__() repr或者交互式解释器--->obj.__repr__() 如果__str__没有被定义,那么就会使用__repr__来代替输出 注意:这俩方法的返回值必须是字符串,否则抛出异常 ''' print(format(s1,'nat')) print(format(s1,'tna')) print(format(s1,'tan')) print(format(s1,'asfdasdffd'))
class B: def __str__(self): return 'str : class B' def __repr__(self): return 'repr : class B' b=B() print('%s'%b) print('%r'%b)
item系列
__getitem__\__setitem__\__delitem__
class Foo: def __init__(self,name): self.name=name def __getitem__(self, item): print(self.__dict__[item]) def __setitem__(self, key, value): self.__dict__[key]=value def __delitem__(self, key): print('del obj[key]时,我执行') self.__dict__.pop(key) def __delattr__(self, item): print('del obj.key时,我执行') self.__dict__.pop(item) f1=Foo('sb') f1['age']=18 f1['age1']=19 del f1.age1 del f1['age'] f1['name']='alex' print(f1.__dict__)
__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。
class Foo: def __del__(self): print('执行我啦') f1=Foo() del f1 print('------->') #输出结果 执行我啦 ------->
__new__
class A: def __init__(self): self.x = 1 print('in init function') def __new__(cls, *args, **kwargs): print('in new function') return object.__new__(A) a = A() print(a.x)
class Singleton: def __new__(cls, *args, **kw): if not hasattr(cls, '_instance'): cls._instance = object.__new__(cls) 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)
__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__
with和__enter__,__exit__
class A: def __enter__(self): print('before') def __exit__(self, exc_type, exc_val, exc_tb): print('after') with A() as a: print('123')
class A: def __init__(self): print('init') def __enter__(self): print('before') def __exit__(self, exc_type, exc_val, exc_tb): print('after') with A() as a: print('123')
class Myfile: def __init__(self,path,mode='r',encoding = 'utf-8'): self.path = path self.mode = mode self.encoding = encoding def __enter__(self): self.f = open(self.path, mode=self.mode, encoding=self.encoding) return self.f def __exit__(self, exc_type, exc_val, exc_tb): self.f.close() with Myfile('file',mode='w') as f: f.write('wahaha')
import pickle class MyPickledump: def __init__(self,path): self.path = path def __enter__(self): self.f = open(self.path, mode='ab') return self def dump(self,content): pickle.dump(content,self.f) def __exit__(self, exc_type, exc_val, exc_tb): self.f.close() class Mypickleload: def __init__(self,path): self.path = path def __enter__(self): self.f = open(self.path, mode='rb') return self def __exit__(self, exc_type, exc_val, exc_tb): self.f.close() def load(self): return pickle.load(self.f) def loaditer(self): while True: try: yield self.load() except EOFError: break # with MyPickledump('file') as f: # f.dump({1,2,3,4}) with Mypickleload('file') as f: for item in f.loaditer(): print(item)
import pickle class MyPickledump: def __init__(self,path): self.path = path def __enter__(self): self.f = open(self.path, mode='ab') return self def dump(self,content): pickle.dump(content,self.f) def __exit__(self, exc_type, exc_val, exc_tb): self.f.close() class Mypickleload: def __init__(self,path): self.path = path def __enter__(self): self.f = open(self.path, mode='rb') return self def __exit__(self, exc_type, exc_val, exc_tb): self.f.close() def __iter__(self): while True: try: yield pickle.load(self.f) except EOFError: break # with MyPickledump('file') as f: # f.dump({1,2,3,4}) with Mypickleload('file') as f: for item in f: print(item)
__len__
class A: def __init__(self): self.a = 1 self.b = 2 def __len__(self): return len(self.__dict__) a = A() print(len(a))
__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)