面向对象双下划线方法

1|0阅读目录

• isinstance和issubclass
• 反射
• 　　setattr
• 　　delattr
• 　　getattr
• 　　hasattr
• __str__和__repr__
• item系列
• 　　__getitem__
• 　　__setitem__
• 　　__delitem__
• __del__
• __new__
• __call__
• with和__enter__,__exit__
• __len__
• __hash__
• __eq__

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2|0isinstance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)

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3|0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.
</span><span style="color: #800000;">"""</span>
<span style="color: #0000ff;">pass</span></pre>

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.
</span><span style="color: #800000;">"""</span>
<span style="color: #0000ff;">pass</span></pre>

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''
</span><span style="color: #800000;">"""</span>
<span style="color: #0000ff;">pass</span></pre>

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''
</span><span style="color: #800000;">"""</span>
<span style="color: #0000ff;">pass</span></pre>

class Foo:
    f = '类的静态变量'
    def __init__(self,name,age):
        self.name=name
        self.age=age
</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> say_hi(self):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">'</span><span style="color: #800000;">hi,%s</span><span style="color: #800000;">'</span>%<span style="color: #000000;">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 </span>= <span style="color: #800000;">"</span><span style="color: #800000;">old boy</span><span style="color: #800000;">"</span>

<span style="color: #0000ff;">def</span> <span style="color: #800080;">__init__</span><span style="color: #000000;">(self):
    self.name </span>= <span style="color: #800000;">'</span><span style="color: #800000;">wupeiqi</span><span style="color: #800000;">'</span>

<span style="color: #0000ff;">def</span><span style="color: #000000;"> func(self):
    </span><span style="color: #0000ff;">return</span> <span style="color: #800000;">'</span><span style="color: #800000;">func</span><span style="color: #800000;">'</span><span style="color: #000000;">

@staticmethod
</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> bar():
    </span><span style="color: #0000ff;">return</span> <span style="color: #800000;">'</span><span style="color: #800000;">bar</span><span style="color: #800000;">'</span>

print getattr(Foo, 'staticField')

print getattr(Foo, 'func')

print getattr(Foo, 'bar')

#!/usr/bin/env python
# -*- coding:utf-8 -*-
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')()

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4|0__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
</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__repr__</span><span style="color: #000000;">(self):
    </span><span style="color: #0000ff;">return</span> <span style="color: #800000;">'</span><span style="color: #800000;">School(%s,%s)</span><span style="color: #800000;">'</span> %<span style="color: #000000;">(self.name,self.addr)
</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__str__</span><span style="color: #000000;">(self):
    </span><span style="color: #0000ff;">return</span> <span style="color: #800000;">'</span><span style="color: #800000;">(%s,%s)</span><span style="color: #800000;">'</span> %<span style="color: #000000;">(self.name,self.addr)

</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__format__</span><span style="color: #000000;">(self, format_spec):
    </span><span style="color: #008000;">#</span><span style="color: #008000;"> if format_spec</span>
    <span style="color: #0000ff;">if</span> <span style="color: #0000ff;">not</span> format_spec <span style="color: #0000ff;">or</span> format_spec <span style="color: #0000ff;">not</span> <span style="color: #0000ff;">in</span><span style="color: #000000;"> format_dict:
        format_spec</span>=<span style="color: #800000;">'</span><span style="color: #800000;">nat</span><span style="color: #800000;">'</span><span style="color: #000000;">
    fmt</span>=<span style="color: #000000;">format_dict[format_spec]
    </span><span style="color: #0000ff;">return</span> fmt.format(obj=<span style="color: #000000;">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:
 </span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__str__</span><span style="color: #000000;">(self):
     </span><span style="color: #0000ff;">return</span> <span style="color: #800000;">'</span><span style="color: #800000;">str : class B</span><span style="color: #800000;">'</span>

 <span style="color: #0000ff;">def</span> <span style="color: #800080;">__repr__</span><span style="color: #000000;">(self):
     </span><span style="color: #0000ff;">return</span> <span style="color: #800000;">'</span><span style="color: #800000;">repr : class B</span><span style="color: #800000;">'</span><span style="color: #000000;">

b=B()

print('%s'%b)

print('%r'%b)

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5|0item系列

__getitem__\__setitem__\__delitem__

class Foo:
    def __init__(self,name):
        self.name=name
</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__getitem__</span><span style="color: #000000;">(self, item):
    </span><span style="color: #0000ff;">print</span>(self.<span style="color: #800080;">__dict__</span><span style="color: #000000;">[item])

</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__setitem__</span><span style="color: #000000;">(self, key, value):
    self.</span><span style="color: #800080;">__dict__</span>[key]=<span style="color: #000000;">value
</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__delitem__</span><span style="color: #000000;">(self, key):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">'</span><span style="color: #800000;">del obj[key]时,我执行</span><span style="color: #800000;">'</span><span style="color: #000000;">)
    self.</span><span style="color: #800080;">__dict__</span><span style="color: #000000;">.pop(key)
</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__delattr__</span><span style="color: #000000;">(self, item):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">'</span><span style="color: #800000;">del obj.key时,我执行</span><span style="color: #800000;">'</span><span style="color: #000000;">)
    self.</span><span style="color: #800080;">__dict__</span><span style="color: #000000;">.pop(item)

f1=Foo('sb')

f1['age']=18

f1['age1']=19

del f1.age1

del f1['age']

f1['name']='alex'

print(f1.dict)

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6|0__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:
</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__del__</span><span style="color: #000000;">(self):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">'</span><span style="color: #800000;">执行我啦</span><span style="color: #800000;">'</span><span style="color: #000000;">)

f1=Foo()

del f1

print('------->')
#输出结果

执行我啦

------->

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7|0__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)
单例模式

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8|0__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:
</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__init__</span><span style="color: #000000;">(self):
    </span><span style="color: #0000ff;">pass</span>

<span style="color: #0000ff;">def</span> <span style="color: #800080;">__call__</span>(self, *args, **<span style="color: #000000;">kwargs):

    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">'</span><span style="color: #800000;">__call__</span><span style="color: #800000;">'</span><span style="color: #000000;">)

obj = Foo() # 执行 init

obj()       # 执行 call

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9|0with和__enter__,__exit__

class A:
    def __enter__(self):
        print('before')
def __exit__(self, exc_type, exc_val, exc_tb):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #ff0000;">'</span><span style="color: #ff0000;">after</span><span style="color: #ff0000;">'</span><span style="color: #000000;">)

with A() as a:

print('123')

class A:
    def __init__(self):
        print('init')
def __enter__(self):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #ff0000;">'</span><span style="color: #ff0000;">before</span><span style="color: #ff0000;">'</span><span style="color: #000000;">)

def __exit__(self, exc_type, exc_val, exc_tb):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #ff0000;">'</span><span style="color: #ff0000;">after</span><span style="color: #ff0000;">'</span><span style="color: #000000;">)

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 </span><span style="color: #808080;">=</span> <span style="color: #0000ff;">open</span>(self.path, mode<span style="color: #808080;">=</span>self.mode, encoding<span style="color: #808080;">=</span><span style="color: #000000;">self.encoding)
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> self.f

def __exit__(self, exc_type, exc_val, exc_tb):
    self.f.</span><span style="color: #0000ff;">close</span><span style="color: #000000;">()

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 </span><span style="color: #808080;">=</span> <span style="color: #0000ff;">open</span>(self.path, mode<span style="color: #808080;">=</span><span style="color: #ff0000;">'</span><span style="color: #ff0000;">ab</span><span style="color: #ff0000;">'</span><span style="color: #000000;">)
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> self

def </span><span style="color: #0000ff;">dump</span><span style="color: #000000;">(self,content):
    pickle.</span><span style="color: #0000ff;">dump</span><span style="color: #000000;">(content,self.f)

def __exit__(self, exc_type, exc_val, exc_tb):
    self.f.</span><span style="color: #0000ff;">close</span><span style="color: #000000;">()

class Mypickleload:

def init(self,path):

self.path = path
def __enter__(self):
    self.f </span><span style="color: #808080;">=</span> <span style="color: #0000ff;">open</span>(self.path, mode<span style="color: #808080;">=</span><span style="color: #ff0000;">'</span><span style="color: #ff0000;">rb</span><span style="color: #ff0000;">'</span><span style="color: #000000;">)
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> self


def __exit__(self, exc_type, exc_val, exc_tb):
    self.f.</span><span style="color: #0000ff;">close</span><span style="color: #000000;">()

def </span><span style="color: #0000ff;">load</span><span style="color: #000000;">(self):
     </span><span style="color: #0000ff;">return</span> pickle.<span style="color: #0000ff;">load</span><span style="color: #000000;">(self.f)


def loaditer(self):
    </span><span style="color: #0000ff;">while</span><span style="color: #000000;"> True:
        try:
            yield  self.</span><span style="color: #0000ff;">load</span><span style="color: #000000;">()
        </span><span style="color: #0000ff;">except</span><span style="color: #000000;"> EOFError:
            </span><span style="color: #0000ff;">break</span><span style="color: #000000;">

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 </span><span style="color: #808080;">=</span> <span style="color: #0000ff;">open</span>(self.path, mode<span style="color: #808080;">=</span><span style="color: #ff0000;">'</span><span style="color: #ff0000;">ab</span><span style="color: #ff0000;">'</span><span style="color: #000000;">)
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> self

def </span><span style="color: #0000ff;">dump</span><span style="color: #000000;">(self,content):
    pickle.</span><span style="color: #0000ff;">dump</span><span style="color: #000000;">(content,self.f)

def __exit__(self, exc_type, exc_val, exc_tb):
    self.f.</span><span style="color: #0000ff;">close</span><span style="color: #000000;">()

class Mypickleload:

def init(self,path):

self.path = path
def __enter__(self):
    self.f </span><span style="color: #808080;">=</span> <span style="color: #0000ff;">open</span>(self.path, mode<span style="color: #808080;">=</span><span style="color: #ff0000;">'</span><span style="color: #ff0000;">rb</span><span style="color: #ff0000;">'</span><span style="color: #000000;">)
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> self


def __exit__(self, exc_type, exc_val, exc_tb):
    self.f.</span><span style="color: #0000ff;">close</span><span style="color: #000000;">()

def __iter__(self):
    </span><span style="color: #0000ff;">while</span><span style="color: #000000;"> True:
        try:
            yield  pickle.</span><span style="color: #0000ff;">load</span><span style="color: #000000;">(self.f)
        </span><span style="color: #0000ff;">except</span><span style="color: #000000;"> EOFError:
            </span><span style="color: #0000ff;">break</span><span style="color: #000000;">

with MyPickledump('file') as f:
f.dump({1,2,3,4})
with Mypickleload('file') as f:

for item in f:

print(item)

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10|0__len__

class A:
    def __init__(self):
        self.a = 1
        self.b = 2
<span style="color: #0000ff;">def</span> <span style="color: #800080;">__len__</span><span style="color: #000000;">(self):
    </span><span style="color: #0000ff;">return</span> len(self.<span style="color: #800080;">__dict__</span><span style="color: #000000;">)

a = A()

print(len(a))

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11|0__hash__

class A:
    def __init__(self):
        self.a = 1
        self.b = 2
<span style="color: #0000ff;">def</span> <span style="color: #800080;">__hash__</span><span style="color: #000000;">(self):
    </span><span style="color: #0000ff;">return</span> hash(str(self.a)+<span style="color: #000000;">str(self.b))

a = A()

print(hash(a))

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12|0__eq__

class A:
    def __init__(self):
        self.a = 1
        self.b = 2
<span style="color: #0000ff;">def</span> <span style="color: #800080;">__eq__</span><span style="color: #000000;">(self,obj):
    </span><span style="color: #0000ff;">if</span>  self.a == obj.a <span style="color: #0000ff;">and</span> self.b ==<span style="color: #000000;"> obj.b:
        </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> True

a = A()

b = A()

print(a == b)

class FranchDeck:
    ranks = [str(n) for n in range(2,11)] + list('JQKA')
    suits = ['红心','方板','梅花','黑桃']
</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__init__</span><span style="color: #000000;">(self):
    self._cards </span>= [Card(rank,suit) <span style="color: #0000ff;">for</span> rank <span style="color: #0000ff;">in</span><span style="color: #000000;"> FranchDeck.ranks
                                    </span><span style="color: #0000ff;">for</span> suit <span style="color: #0000ff;">in</span><span style="color: #000000;"> FranchDeck.suits]

</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__len__</span><span style="color: #000000;">(self):
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> len(self._cards)

</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__getitem__</span><span style="color: #000000;">(self, item):
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> self._cards[item]

deck = FranchDeck()

print(deck[0])

from random import choice

print(choice(deck))

print(choice(deck))

class FranchDeck:
    ranks = [str(n) for n in range(2,11)] + list('JQKA')
    suits = ['红心','方板','梅花','黑桃']
</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__init__</span><span style="color: #000000;">(self):
    self._cards </span>= [Card(rank,suit) <span style="color: #0000ff;">for</span> rank <span style="color: #0000ff;">in</span><span style="color: #000000;"> FranchDeck.ranks
                                    </span><span style="color: #0000ff;">for</span> suit <span style="color: #0000ff;">in</span><span style="color: #000000;"> FranchDeck.suits]

</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__len__</span><span style="color: #000000;">(self):
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> len(self._cards)

</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__getitem__</span><span style="color: #000000;">(self, item):
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> self._cards[item]

</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__setitem__</span><span style="color: #000000;">(self, key, value):
    self._cards[key] </span>=<span style="color: #000000;"> 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])

class Person:
    def __init__(self,name,age,sex):
        self.name = name
        self.age = age
        self.sex = sex
</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__hash__</span><span style="color: #000000;">(self):
    </span><span style="color: #0000ff;">return</span> hash(self.name+<span style="color: #000000;">self.sex)

</span><span style="color: #0000ff;">def</span> <span style="color: #800080;">__eq__</span><span style="color: #000000;">(self, other):
    </span><span style="color: #0000ff;">if</span> self.name == other.name <span style="color: #0000ff;">and</span> self.sex == other.sex:<span style="color: #0000ff;">return</span><span style="color: #000000;"> True

p_lst = []

for i in range(84):

p_lst.append(Person('egon',i,'male'))
print(p_lst)

print(set(p_lst))