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

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

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

# 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

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