python之路——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): passobj = Foo()
isinstance(obj, Foo)
issubclass(sub, super)检查sub类是否是 super 类的派生类
class Foo(object): passclass Bar(Foo):
passissubclass(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)
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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>
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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>
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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>
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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>
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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)
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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')
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#!/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
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#!/usr/bin/env python # -*- coding:utf-8 -*-def test():
print('from the test')
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#!/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__
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#_*_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'))
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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)
item系列
__getitem__\__setitem__\__delitem__
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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)
__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。
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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
------->
__new__
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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)
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class Singleton: def __new__(cls, *args, **kw): if not hasattr(cls, '_instance'): cls._instance = object.__new__(cls) return cls._instanceone = Singleton()
two = Singleton()two.a = 3
print(one.a)
# 3one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()()
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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
with和__enter__,__exit__
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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')
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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')
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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')
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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;">()
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;">
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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;">()
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;">
__len__
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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))
__hash__
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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))
__eq__
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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)
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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))
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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])
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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))
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