Python __slots__的使用方法

class A(object):
  pass

a = A()
print a.__dict__   #{}
A.name = 'xiaoming' #动态的给实例绑定属性，其实例属性会保存到实例的__dict__中
print a.__dict__   #{'name': 'xiaoming'}
f = lambda :100
a.fun = f      
print a.__dict__   #{'fun': <function <lambda> at>, 'name': 'xiaoming'}

print A.__dict__   #...
f = lambda :100
A.fun = f      
print A.__dict__   #... + 'fun': <function <lambda> at 0x0000000003582978>

class A(object):
  __slots__ = ('age','name')
a = A()
a.name = 'xiaoming'
a.age = 10
a.id = 123456 #error  AttributeError: 'A' object has no attribute 'id'

#!/usr/bin/python
# -*- coding: utf-8 -*-
class Foo(object):
  __slots__ = ('age','name')
  def __init__(self,age = 0):
    self.age = age

s = Foo.__dict__['age']
print s          #<member 'age' of 'Foo' objects>
print type(s)       #<type 'member_descriptor'>
'''证明为数据描述符'''
print '__get__' in dir(s) #True
print '__set__' in dir(s) #True

f1 = Foo(1)
f2 = Foo(2)
print f1.age,f2.age          #1,2
print Foo.__dict__['age'].__get__(f1) #1
print Foo.__dict__['age'].__get__(f2) #2

class A(object):
  pass

class B(object):
  __slots__ = ('age','name')

a = A()
b = B()

print a.__dict__ #{}
print A.__dict__ 
'''
{'__dict__': <attribute '__dict__' of 'A' objects>, '__module__': '__main__', '__weakref__': <attribute '__weakref__' of 'A' objects>, '__doc__': None}
'''

print b.__dict__ #AttributeError: 'B' object has no attribute '__dict__'
print B.__dict__
'''
{'age': <member 'age' of 'B' objects>, '__module__': '__main__', '__doc__': None, '__slots__': ('age', 'name'), 'name': <member 'name' of 'B' objects>}
'''  

class Foo(object):
  __slots__ = ('age','name')

class F1(Foo):
  pass

class F2(Foo):
  __slots__ = ()

f1,f2 = F1(),F2()
f1.a = 1
f2.a = 1    #AttributeError: 'F2' object has no attribute 'a'
f2.age = 1

f = Foo()
print f.age  #AttributeError: age
f.age = 1
print f.age  #1

f = Foo()
Foo.xx = 1
print f.xx   #1

class Foo(object):
  __slots__ = ('age','name')
  age = 10
  def __init__(self):
    self.name = 'xiaoming'
f = Foo()
print f.name     #'xiaoming'
print f.age     #10
f.name = 'xiaohong' 

#f.age = 12     #AttributeError: 'Foo' object attribute 'age' is read-only

Foo.age = 12     #正确
print f.name     #'xiaohong'
print f.age     #12


#del f.age      #AttributeError: 'Foo' object attribute 'age' is read-only


#del f.name 调用的是描述符方法__delete__,应该是将描述符中存储的实例与值的映射删除了

del f.name      #实例属性的删除还是可以的,但是删除的并不是类字典中的name属性
print f.name     #AttributeError: name

del Foo.age     #通过类来删除类属性还是可以的,不过这样会影响该类的所有实例
print f.age     #AttributeError: 'Foo' object has no attribute 'age'