Python--040类和对象：一些相关的BIF

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Tip：


一，理论

二，应用
1  issubclass(class, classinfo)
>>> class A:
        pass

>>> class B(A):
        pass

>>> issubclass(A, B)
False
>>> issubclass(B, A)
True

2 isinstance(object, classinfo)         #第一个不是object，永远传回false，第二个不是class类型，会有TypeError异常
>>> isinstance(B, A)
False
>>> b1 = B()
>>> isinstance(b1, B)
True
>>> isinstance(b1, b1)
Traceback (most recent call last):
  File "<pyshell#15>", line 1, in <module>
    isinstance(b1, b1)
TypeError: isinstance() arg 2 must be a type or tuple of types

3 hasattr(object, name)  #name必须为字符串形式
>>> 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 "<pyshell#25>", line 1, in <module>
    hasattr(c1, x)
NameError: name 'x' is not defined

4 getattr(object, name[, default])
>>> getattr(c1, 'x')
0
>>> getattr(c1, 'y')
Traceback (most recent call last):
  File "<pyshell#27>", line 1, in <module>
    getattr(c1, 'y')
AttributeError: 'C' object has no attribute 'y'
>>> getattr(c1, 'y','访问不存在')
'访问不存在'

5 setattr(object, name, value)
>>> setattr(c1, 'y', 'FishC')
>>> getattr(c1, 'y','访问不存在')
'FishC'

6 delattr(object, name)
>>> delattr(c1, 'y')
>>> delattr(c1, 'y')
Traceback (most recent call last):
  File "<pyshell#32>", line 1, in <module>
    delattr(c1, 'y')
AttributeError: y

7 property(getattr, setattr, delattr, doc)
>>> class C:
        def __init__(self, size = 10):
                self.size = size
        def getattr(self):
                return self.size
        def setattr(self, size):
                self.size = size
        def delattr(self):
                del self.size
        x = property(getattr, setattr, delattr)

       
>>> c1 = C()
>>> c1.getattr()
10
>>> c1.x
10
>>> c1.x = 20
>>> c1.x
20
>>> del c1.x
>>> c1.x
Traceback (most recent call last):
  File "<pyshell#54>", line 1, in <module>
    c1.x
  File "<pyshell#47>", line 5, in getattr
    return self.size
AttributeError: 'C' object has no attribute 'size'

三，课后练习