python24 跟类相关的BIF

1. issubclass(class,classinfo)

　　一个类被认为是其自身的子类

　　classinfo可以是类对象组成的元组，只要class与其中任何一个候选类的子类，则返回True

　　其他情况TypeError

>>> class A():
...     pass
...
>>> class B(A):
...     pass
...
>>> issubclass(B,A)
True
>>> issubclass(B,B)
True
>>> issubclass(A,B)
False
>>> issubclass(A,object)
True

2. isinstance(object, classinfo)

　1.如果第一参数不是对象，则永远返回False

　2.如果第二个参数不是类或者由类对象组成的元组，会抛出一个TypeError异常

>>> b1 = B()
>>> isinstance(b1,B)
True
>>> isinstance(b1,A)
True
>>> isinstance(b1,C)
False
>>> isinstance(b1,(A,B,C))
True

3.hasattr(object,name)

　attr = attribute : 属性

　测试对象是否有相应的属性

>>> class C:
...     def __init__(self,x=0):
...             self.x = x
...
>>> c1 = C()
>>> hasattr(c1,‘x‘)
True
>>> hasattr(c1,x)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name ‘x‘ is not defined

4.getattr(object,name[,default])

　访问对象的属性值，如果不存在返回设置的默认值,否则会抛出AttrubuteError

>>> getattr(c1,‘x‘)
0
>>> getattr(c1,‘y‘,‘您所访问的属性不存在...‘)
‘您所访问的属性不存在...‘

5.setattr(object,name,value)

　设置对象的属性值，如果不存在，将创建属性并赋值

>>> setattr(c1, ‘x‘, ‘5‘)
>>> getattr(c1, ‘x‘)
‘5‘
>>> setattr(c1, ‘y‘, ‘10‘)
>>> getattr(c1, ‘y‘)
‘10‘

6.delattr(object, name)

>>> delattr(c1,‘y‘)
>>> getattr(c1,‘y‘,‘访问属性不存在‘)
‘访问属性不存在‘

7.property(fget = None, fset = None, fdel = None, doc = None)

　　作用:通过属性设置属性

>>> class C:
...     def __init__(self,size = 10):
...             self.size = size
...     def getSize(self):
...             return self.size
...     def setSize(self,value):
...             self.size = value
...     def delSize(self):
...             del self.size
...     x = property(getSize, setSize, delSize)
...
>>> c1 = C()
>>> c1.getSize()
10
>>> c1.x
10
>>> c1.x = 18
>>> c1.x
18
>>> c1.size
18
>>> c1.getSize()
18

　>>> del c1.x
　>>> c1.size
　Traceback (most recent call last):
　File "<stdin>", line 1, in <module>
　AttributeError: ‘C‘ object has no attribute ‘size‘