python hasattr/getattr/setattr介绍

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摘要

Python 对应属性和方法的判断 hasattr/getattr/setattr

hasattr

判断一个对象里面是否有name属性或者方法，返回值为Boolean值， 有name 返回true，反之false
其等同于getattr(object, name)

hasattr(object, name)

getattr

类似于hasattr(object, name)，但是getattr当name不存在于object的时候返回default值。否则返回实际的值

getattr(object, name[, default])

setattr

给对象的属性复制，如果属性不存在，则先创建再赋值

setattr(object, name, value)

examples

root@pts/1 $ python
Python 3.5.3 (default, Jul 20 2017, 16:49:29)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-11)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> help(getattr)

>>>

## 定义测试类
>>> class TestAttr():
...     name = 'James'
...
...     def sayHello(self):
...         return 'Hello James'
...
>>> ta = TestAttr()

## ta为object对象类型
>>> ta
<__main__.TestAttr object at 0x7f52d55df5f8>

## hasattr 测试， name属性必须加引号
>>> hasattr(ta, name)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'name' is not defined
>>> hasattr(ta, "name")
True
>>> hasattr(ta, "sayHello")
True

## hasattr 不能像getattr 那样调用函数
>>> hasattr(ta, "sayHello")()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'bool' object is not callable
>>>

## setattr测试，当不存在属性的时候可以创建属性
>>> hasattr(ta, "age")
False
>>> setattr(ta, "age", 28)
>>> hasattr(ta, "age")
True
>>>

## getattr 测试
>>> getattr(ta, "name")
'James'

## 是函数的时候，可以调用函数
>>> getattr(ta, "sayHello")
<bound method TestAttr.sayHello of <__main__.TestAttr object at 0x7f52d55df5f8>>
>>> getattr(ta, "sayHello")()
'Hello James'
>>> getattr(ta, "age")
28

## 不存在的时候得到默认值
>>> getattr(ta, "age2", 18)
18
>>>

Note & Refer to:

从上面的例子中我们看到

• name 参数必须是加引号，不然报错
• name 为函数的时候，调用getattr(object, name)() 相当于 object.name 调用该name函数

例子用法参考官网地址：

• hasattr - https://docs.python.org/3.5/library/functions.html#hasattr
• getattr - https://docs.python.org/3.5/library/functions.html#getattr
• setattr - https://docs.python.org/3.5/library/functions.html#setattr