面向对象进阶
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
以下实例展示了 hasattr 的使用方法：
#!/usr/bin/python# -*- coding: UTF-8 -*- class Coordinate:
x = 10 y = -5 z = 0 point1 = Coordinate() print(hasattr(point1, 'x'))print(hasattr(point1, 'y'))print(hasattr(point1, 'z'))print(hasattr(point1, 'no')) # 没有该属性
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
以下实例展示了 getattr 的使用方法：
>>>class A(object):
... bar = 1...
>>> a = A()>>> getattr(a, 'bar') # 获取属性 bar 值1>>> getattr(a, 'bar2') # 属性 bar2 不存在，触发异常Traceback (most recent call last):
File "<stdin>", line 1, in <module>AttributeError: 'A' object has no attribute 'bar2'>>> getattr(a, 'bar2', 3) # 属性 bar2 不存在，但设置了默认值3
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
以下实例展示了 setattr() 函数的使用方法：
实例一
>>>class A(object):
... bar = 1...
>>> a = A()>>> getattr(a, 'bar') # 获取属性 bar 值1>>> setattr(a, 'bar', 5) # 设置属性 bar 值>>> a.bar5
实例二
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
以下实例展示了 delattr 的使用方法：实例一class Coordinate:
x = 10 y = -5 z = 0 point1 = Coordinate()
print('x = ',point1.x)print('y = ',point1.y)print('z = ',point1.z) delattr(Coordinate, 'z') print('--删除 z 属性后--')print('x = ',point1.x)print('y = ',point1.y) # 触发错误print('z = ',point1.z)
实例二
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__)
实例三
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') #获取到属性值print getattr(Foo, 'func') #获取到func的地址print getattr(Foo, 'bar')
实例四
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
def test():
print('from the test')
"""
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)
__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 f1print('------->')#输出结果执行我啦
------->
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
print("f1['age']=18时,我执行")
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')
# __dict__[item] 内部是以字典的形式保存数据
# __setitem__设置 key, value
f1['age']=18
f1['age1']=19
# __getitem__ 输出设置的值
print(f1.age)
# __delattr__ 根据Key删除设置的属性
del f1.age1
# __delitem__ 根据value删除设置的属性
del f1['age']
f1['name']='alex'
print(f1.__dict__)
__new__
View Code
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)
单例模式
class Singleton:
def __new__(cls, *args, **kw):
if not hasattr(cls, '_instance'):
cls._instance = object.__new__(cls, *args, **kw)
return cls._instance
one = Singleton()
two = Singleton()
two.a = 3print(one.a)# 3
# one和two完全相同,可以用id(), ==, is检测print(id(one))# 29097904print(id(two))# 29097904print(one == two)# Trueprint(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__
__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)
纸牌游戏
from collections import namedtuple
Card = namedtuple('Card',['rank','suit'])
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 choiceprint(choice(deck))print(choice(deck))
纸牌游戏2
from collections import namedtuple
Card = namedtuple('Card',['rank','suit'])
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])
一道面试题
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))