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[ python ] hasattr()、getattr()、setattr() 三者关系及运用

时间:2018-04-26 12:26:00      阅读:193      评论:0      收藏:0      [点我收藏+]

标签:解耦   put   trace   反射   color   场景   traceback   ...   需要   

 hasattr(object, name)

    判断一个对象(object)是否存在name属性或方法,返回boolean值,有name属性返回True, 否则返回False

In [1]: class Test(object):
   ...:     name = ‘hkey‘
   ...:     def hello(self):
   ...:         print(‘hello‘, self.name)
   ...:

In [2]: t = Test()

In [3]: print(hasattr(t, ‘name‘))		# 注意:属性‘name‘是需要引号引起来的
True

In [4]: print(hasattr(t, ‘hello‘))		# 方法也是类的属性
True

 

 getattr(object, name[, default])

    获取对象object的属性或方法(name), 如果存在打印出来,如果不存在,打印默认值,默认值可选,默认值不存在报错对象没有该属性;

In [1]: class Test(object):
   ...:     name = ‘hkey‘
   ...:     def hello(self):
   ...:         print(‘hello ‘, self.name)
   ...:

In [2]: t = Test()

In [3]: print(getattr(t, ‘name‘))
hkey

In [4]: print(getattr(t, ‘hello‘))
<bound method Test.hello of <__main__.Test object at 0x000001499524EE80>>

In [5]: print(getattr(t, ‘age‘))
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-5-bd4a642cfb8c> in <module>()
----> 1 print(getattr(t, ‘age‘)) 	# 没有该属性或方法

AttributeError: ‘Test‘ object has no attribute ‘age‘

In [6]: print(getattr(t, ‘age‘, 20)) 	# 设置默认值
20

 

 setattr(object, name, values)

    给对象的属性赋值,若属性不存在,先创建再赋值

# object不存在属性(age), 用 setattr 新增属性 ‘age‘
In [1]: class Test(object):
   ...:     name = ‘hkey‘
   ...:     def hello(self):
   ...:         print(‘hello ‘, self.name)
   ...:

In [2]: t = Test()

In [3]: print(hasattr(t, ‘age‘))
False

In [4]: setattr(t, ‘age‘, 20)

In [5]: print(hasattr(t, ‘age‘))
True

In [6]: print(getattr(t, ‘age‘))
20


# object 存在属性(name), 用 setattr 覆盖原属性值
In [1]: class Test(object):
   ...:     name = ‘hkey‘
   ...:     def hello(self):
   ...:         print(‘hello ‘, self.name)
   ...:

In [2]: t = Test()

In [3]: print(hasattr(t, ‘name‘)) 	# 使用 hasattr 检查object 是否存在‘name‘属性, True为存在
True

In [4]: setattr(t, ‘name‘, ‘superman‘) 	# setattr 重新为‘name‘属性赋值为‘superman‘

In [5]: print(getattr(t, ‘name‘)) 	# 使用getattr 获取‘name‘属性的值
superman

In [6]: print(t.name) 	# 直接调用实例‘t‘的name属性
superman

 

从上面的实例发现,如果object已经存在属性,再次使用setattr为该属性赋值,该属性会发生变化,这里值得注意。

 

 hasattr(), getattr(), setattr() 使用场景

 * 作为反射对程序进行解耦操作 *

In [1]: class Test(object):
   ...:     def __init__(self):
   ...:         self.x = 1
   ...:         self.y = 2
   ...:
   ...:     def sum(self):
   ...:         print(self.x + self.y)
   ...:
   ...:     def sub(self):
   ...:         print(self.x - self.y)
   ...:

In [2]: t = Test()

In [3]: while True:
   ...:     cmd = input(‘-->‘).strip()
   ...:     if hasattr(t, cmd): 	# ‘hasattr‘ 判断 ‘cmd‘ 属性是否存在
   ...:         func = getattr(t, cmd) 	# getattr 获取 ‘cmd‘ 属性的值
   ...:         func() 	# 执行该属性
   ...:     else:
   ...:         setattr(t, cmd, t.sum) 	# 如果输入不存在的属性名, 使用 ‘setattr‘ 重新为 ‘cmd‘ 赋值为 ‘t.sum‘ 
   ...:         func = getattr(t, cmd)  # getattr 获取 ‘cmd‘ 属性的值
   ...:         func() 	# 执行该属性
   ...:

# 执行结果:
-->sum
3
-->sub
-1
-->dddddd
3

 

[ python ] hasattr()、getattr()、setattr() 三者关系及运用

标签:解耦   put   trace   反射   color   场景   traceback   ...   需要   

原文地址:https://www.cnblogs.com/hukey/p/8949885.html

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