Python反射和内置方法重写操作详解

本文实例讲述了Python反射和内置方法重写操作。分享给大家供大家参考，具体如下：

isinstance和issubclass

isinstance(obj,cls)检查是否obj是否是类 cls 的对象，类似 type()

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。

四个反射函数

hasattr(obj,str)检测是否含有某属性

getattr(obj,str)获取属性,不存在报错

setattr(obj,str,value)设置属性

delattr(obj,str)删除属性,不存在报错

导入其他模块，利用反射查找该模块是否存在某个方法

def test():
 print('from the test')

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__)

运行结果：

del obj.key时,我执行
del obj[key]时,我执行
{'name': 'alex'}

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, *args, **kwargs)
a = A()
print(a.x)

运行结果：

in new function
in init function
1

单例模式：

class A:
 def __new__(cls):
  if not hasattr(cls,'obj'):
   cls.obj = object.__new__(cls)
  return cls.obj
a = A()
b = A()
print(a is b)

运行结果：

True

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__

运行输出：

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))

运行结果：

2

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))

运行结果：

-1777982230

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)

运行结果：

True

合并名字性别一样的人：

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))

运行结果：

[<main.Person object at 0x01425AB0>, <main.Person object at 0x01425AD0>, <main.Person object at 0x01425AF0>, <main.Person object at 0x01425910>, <main.Person object at 0x014258D0>, <main.Person object at 0x01425950>, <main.Person object at 0x01425970>,

<main.Person object at 0x014259D0>, <main.Person object at 0x01425C70>, <main.Person object at 0x01425890>, <main.Person object at 0x01425B30>, <main.Person object at 0x01425BB0>, <main.Person object at 0x01425C30>, <main.Person object at 0x01429710>,

<main.Person object at 0x01429730>, <main.Person object at 0x014298F0>, <main.Person object at 0x01429910>, <main.Person object at 0x01429930>, <main.Person object at 0x01429950>, <main.Person object at 0x01429970>, <main.Person object at 0x01429990>,

<main.Person object at 0x014299B0>, <main.Person object at 0x014299D0>, <main.Person object at 0x014299F0>, <main.Person object at 0x01429A10>, <main.Person object at 0x01429A30>, <main.Person object at 0x01429A50>, <main.Person object at 0x01429A70>,

<main.Person object at 0x01429A90>, <main.Person object at 0x01429AB0>, <main.Person object at 0x01429AD0>, <main.Person object at 0x01429AF0>, <main.Person object at 0x01429B10>, <main.Person object at 0x01429B30>, <main.Person object at 0x01429B50>,

<main.Person object at 0x01429B70>, <main.Person object at 0x01429B90>, <main.Person object at 0x01429BB0>, <main.Person object at 0x01429BD0>, <main.Person object at 0x01429BF0>, <main.Person object at 0x01429C10>, <main.Person object at 0x01429C30>,

<main.Person object at 0x01429C50>, <main.Person object at 0x01429C70>, <main.Person object at 0x01429C90>, <main.Person object at 0x01429CB0>, <main.Person object at 0x01429CD0>, <main.Person object at 0x01429CF0>, <main.Person object at 0x01429D10>,

<main.Person object at 0x01429D30>, <main.Person object at 0x01429D50>, <main.Person object at 0x01429D70>, <main.Person object at 0x01429D90>, <main.Person object at 0x01429DB0>, <main.Person object at 0x01429DD0>, <main.Person object at 0x01429DF0>,

<main.Person object at 0x01429E10>, <main.Person object at 0x01429E30>, <main.Person object at 0x01429E50>, <main.Person object at 0x01429E70>, <main.Person object at 0x01429E90>, <main.Person object at 0x01429EB0>, <main.Person object at 0x01429ED0>,

<main.Person object at 0x01429EF0>, <main.Person object at 0x01429F10>, <main.Person object at 0x01429F30>, <main.Person object at 0x01429F50>, <main.Person object at 0x01429F70>, <main.Person object at 0x01429F90>, <main.Person object at 0x01429FB0>,

<main.Person object at 0x01429FD0>, <main.Person object at 0x01429FF0>, <main.Person object at 0x01751030>, <main.Person object at 0x01751050>, <main.Person object at 0x01751070>, <main.Person object at 0x01751090>, <main.Person object at 0x017510B0>,

<main.Person object at 0x017510D0>, <main.Person object at 0x017510F0>, <main.Person object at 0x01751110>, <main.Person object at 0x01751130>, <main.Person object at 0x01751150>, <main.Person object at 0x01751170>, <main.Person object at 0x01751190>]
{<main.Person object at 0x01425AB0>}