怎么判断 Python 对象是否包含某个属性？

Question

怎么在使用前判断 Python 对象是否包含某个属性或者某个方法？

class FooClass:
    pass

k = FooClass()
k.someAtt = 2
k.att

输出：

Traceback (most recent call last):
  File "Untitled.py", line 6, in <module>
    k.att
AttributeError: FooClass instance has no attribute 'att'

Answer 1

方法一：通过异常捕捉来实现逻辑

class FooClass:
pass

k = FooClass()
try:
    #do some thing you need
    print k.att
except AttributeError as e:
    #error: has not attribute
    pass 

方法二：调用hasattr方法

hasattr(object, name)
说明：判断对象object是否包含名为name的特性（hasattr是通过调用getattr(ojbect, name)是否抛出异常来实现的）。
参数object：对象。
参数name：特性名称。

>>> hasattr(list, 'append')
True

>>> hasattr(list, 'add')
False

方法三：使用dir方法

objlist = dir(k)
if 'att' in objlist:
    #do some thing you need
    print k.att
else:
    #error: has not attribute
    pass

另外， 这种问题可以使用google搜索下，善用google

Answer 2

dir(FooClass)

Answer 3

http://stackoverflow.com/questions/3681272/can-i-get-a-reference-to-a-python-property
http://stackoverflow.com/questions/191010/how-to-get-a-complete-list-of-objects-methods-and-attributes