python--面向對象(高級)
阿新 • • 發佈:2017-08-20
pen turned true 地址 all -1 == pri 導入
python --面向對象進階
isinstance和 issubclass
isinstance(obj,cls)檢查是否是obj是否是類cls的對象
class Foo(object): pass obj = Foo() sinstance(obj, Foo)
isscubclass(sub,super)檢查sub類是否是super類的派生類
class Foo(object):
pass
class Bar(Foo):
pass
issubclass(Bar, Foo)
反射
什麽是反射
反射的概念是由Smith在1982年首次提出的,主要是指程序可以訪問、檢測和修改它本身狀態或行為的一種能力(自省)。這一概念的提出很快引發了計算機科學領域關於應用反射性的研究。它首先被程序語言的設計領域所采用,並在Lisp和面向對象方面取得了成績。
2 python面向對象中的反射:通過字符串的形式操作對象相關的屬性。python中的一切事物都是對象(都可以使用反射)
四個可以實現自省的函數
下列方法適用於類和對象(一切皆對象,類本身也是一個對象)
hasattr
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
getattr
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
setattr
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
delattr
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
四個方法的使用
class Foo: f = ‘類的靜態變量‘ def __init__(self,name,age): self.name=name self.age=age def say_hi(self): print(‘hi,%s‘%self.name) obj=Foo(‘egon‘,73) #檢測是否含有某屬性 print(hasattr(obj,‘name‘)) print(hasattr(obj,‘say_hi‘)) #獲取屬性 n=getattr(obj,‘name‘) print(n) func=getattr(obj,‘say_hi‘) func() print(getattr(obj,‘aaaaaaaa‘,‘不存在啊‘)) #報錯 #設置屬性 setattr(obj,‘sb‘,True) setattr(obj,‘show_name‘,lambda self:self.name+‘sb‘) print(obj.__dict__) print(obj.show_name(obj)) #刪除屬性 delattr(obj,‘age‘) delattr(obj,‘show_name‘) delattr(obj,‘show_name111‘)#不存在,則報錯 print(obj.__dict__)
類也是對象
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‘)
類也是面向對象
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‘)
導入其他模塊,利用反射查找該模塊是否存在某個方法
#!/usr/bin/env python # -*- coding:utf-8 -*- def test(): print(‘from the test‘)
#!/usr/bin/env python
# -*- coding:utf-8 -*-
"""
程序目錄:
module_test.py
index.py
當前文件:
index.py
"""
import module_test as obj
#obj.test()
print(hasattr(obj,‘test‘))
getattr(obj,‘test‘)()
__str__ 和 __repr__
改變對象的字符串顯示__str__,__repr__
自定制格式化字符串__format__
#_*_coding:utf-8_*_
format_dict={
‘nat‘:‘{obj.name}-{obj.addr}-{obj.type}‘,#學校名-學校地址-學校類型
‘tna‘:‘{obj.type}:{obj.name}:{obj.addr}‘,#學校類型:學校名:學校地址
‘tan‘:‘{obj.type}/{obj.addr}/{obj.name}‘,#學校類型/學校地址/學校名
}
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函數或者print函數--->obj.__str__()
repr或者交互式解釋器--->obj.__repr__()
如果__str__沒有被定義,那麽就會使用__repr__來代替輸出
註意:這倆方法的返回值必須是字符串,否則拋出異常
‘‘‘
print(format(s1,‘nat‘))
print(format(s1,‘tna‘))
print(format(s1,‘tan‘))
rint(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)
%s和%r
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__
析構方法,當對象在內存中被釋放時,自動觸發執行。
註:此方法一般無須定義,因為Python是一門高級語言,程序員在使用時無需關心內存的分配和釋放,因為此工作都是交給Python解釋器來執行,所以,析構函數的調用是由解釋器在進行垃圾回收時自動觸發執行的。
class Foo:
def __del__(self):
print(‘執行我啦‘)
f1=Foo()
del f1
print(‘------->‘)
#輸出結果
執行我啦
------->
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
def __delitem__(self, key):
print(‘del obj[key]時,我執行‘)
self.__dict__.pop(key)
def __delattr__(self, item):
print(‘del obj.key時,我執行‘)
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__)
__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)
class Singleton: def __new__(cls, *args, **kw): if not hasattr(cls, ‘_instance‘): orig = super(Singleton, cls) cls._instance = orig.__new__(cls, *args, **kw) 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檢測 print(id(one)) # 29097904 print(id(two)) # 29097904 print(one == two) # True print(one is two)
__call__
對象後面加括號,觸發執行
註:構造方法的執行是由創建對象觸發的,即:對象=類名();而對於__call__方法的執行是由對象後加括號觸發的,即:對象()
)或者類()()
class Foo:
def __init__(self):
pass
def __call__(self, *args, **kwargs):
print(‘__call__‘)
obj = Foo() # 執行 __init__
obj() # 執行 __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__
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)
class FranchDeck:
ranks = [str(n) for n in range(2,11)] + list(‘JQKA‘)
suits = [‘紅心‘,‘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 choice
print(choice(deck))
print(choice(deck))
class FranchDeck:
ranks = [str(n) for n in range(2,11)] + list(‘JQKA‘)
suits = [‘紅心‘,‘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])
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))
python--面向對象(高級)