python中hasattr()、getattr()、setattr()函数的使用

>>> 
>>> class A():
  name = 'python'
  def func(self):
    return 'A()类的方法func()'
>>> 
>>> hasattr(A, 'name')
True
>>> 
>>> hasattr(A, 'age')
False
>>> 
>>> hasattr(A, 'func')
True
>>>

>>> 
>>> class A():
  name = 'python'
  def func(self):
    return 'Hello world'
>>> 
>>> getattr(A, 'name')
'python'
>>> 
>>> getattr(A, 'age')　　　　# age变量不存在则报错
Traceback (most recent call last):
 File "<pyshell#464>", line 1, in <module>
  getattr(A, 'age')
AttributeError: class A has no attribute 'age'
>>> 
>>> getattr(A, 'age', 20)
>>> 
>>> getattr(A, 'func')
<unbound method A.func>
>>> 
>>> getattr(A, 'func')()　　　　# func()函数不能被A类对象调用，所以报错， 需要用类的实例化对象来调用
Traceback (most recent call last):
 File "<pyshell#470>", line 1, in <module>
  getattr(A, 'func')()
TypeError: unbound method func() must be called with A instance as first argument (got nothing instead)
>>> 
>>> getattr(A(), 'func')()
'Hello world'
>>> 
>>> class A(object):
  　　　　name = 'python'
  　　　　@classmethod
  　　　　def func(cls):
    　　　　　　return 'the method of A object.'
>>> 
>>> getattr(A, 'func')()
'the method of A object.'
>>> 

>>> 
>>> class A():
  name = 'python'
  def func(self):
    return 'Hello world'
>>> 
>>> setattr(A, 'name', 'java')
>>> getattr(A, 'name')
'java'
>>> 
>>> setattr(A, 'age', 20)
>>> getattr(A, 'age')
>>> 

>>> 
>>> class A():
  name = 'python'
  def func(self):
    return 'Hello world'
>>> 
>>> if hasattr(A, 'age'):
  print getattr(A, 'age')
else:
  setattr(A, 'age', 20)
>>> 
>>> getattr(A, 'age')
>>>