property 返回 property 属性
内置函数（类）property，Python 官方文档描述如下：
help(property)
Help on class property in module builtins:
class property(object)
| property(fget=None, fset=None, fdel=None, doc=None)
|
| Property attribute.
|
| fget
| function to be used for getting an attribute value
| fset
| function to be used for setting an attribute value
| fdel
| function to be used for del'ing an attribute
| doc
| docstring
|
| Typical use is to define a managed attribute x:
|
| class C(object):
| def getx(self): return self._x
| def setx(self, value): self._x = value
| def delx(self): del self._x
| x = property(getx, setx, delx, "I'm the 'x' property.")
|
| Decorators make defining new properties or modifying existing ones easy:
|
| class C(object):
| @property
| def x(self):
| "I am the 'x' property."
| return self._x
| @x.setter
| def x(self, value):
| self._x = value
| @x.deleter
| def x(self):
| del self._x
|
返回 property 属性。
fget 是获取属性值的函数。fset 是用于设置属性值的函数。fdel 是用于删除属性值的函数，doc 为属性对象创建文档字符串。
type(property)
type
dir(property)
['__class__',
'__delattr__',
'__delete__',
'__dir__',
'__doc__',
'__eq__',
'__format__',
'__ge__',
'__get__',
'__getattribute__',
'__gt__',
'__hash__',
'__init__',
'__init_subclass__',
'__isabstractmethod__',
'__le__',
'__lt__',
'__ne__',
'__new__',
'__reduce__',
'__reduce_ex__',
'__repr__',
'__set__',
'__setattr__',
'__sizeof__',
'__str__',
'__subclasshook__',
'deleter',
'fdel',
'fget',
'fset',
'getter',
'setter']
一个典型的用法是定义一个托管属性 x:
# 列一
class C:
def __init__(self,value):
self._x = value
def getx(self):
return self._x
def setx(self, value):
self._x = value
def delx(self):
del self._x
x = property(getx, setx, delx, "I'm the 'x' property.")
如果 c 是 C 的实例，c.x 将调用 getter，c.x = value 将调用 setter，del c.x 将调用 deleter。
如果给出，doc 将成为该 property 属性的文档字符串。否则该 property 将拷贝 fget 的文档字符串（如果存在）。
c = C(1)
c.x
1
c.x = 2
c.x
2
del c.x
c.x
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-16-d32ce31f0255> in <module>
1 del c.x
----> 2 c.x
<ipython-input-10-eaaa1d84111b> in getx(self)
4
5 def getx(self):
----> 6 return self._x
7
8 def setx(self, value):
AttributeError: 'C' object has no attribute '_x'
这令使用 property() 作为装饰器来创建只读的特征属性可以很容易地实现:
class Parrot:
def __init__(self):
self._voltage = 100000
@property
def voltage(self):
"""Get the current voltage."""
return self._voltage
以上 @property 装饰器会将 voltage() 方法转化为一个具有相同名称的只读属性的 getter，并将 voltage 的文档字符串设置为 ‘Get the current voltage.’
p = Parrot()
p.voltage
100000
p.voltage = 100
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-20-50ba7917c8b5> in <module>
----> 1 p.voltage = 100
AttributeError: can't set attribute
特征属性对象具有 getter, setter 以及 deleter 方法，它们可用作装饰器来创建该特征属性的副本，并将相应的访问函数设为所装饰的函数。
class C:
def __init__(self,value):
self._x = value
@property
def x(self):
"""I'm the 'x' property."""
return self._x
@x.setter
def x(self, value):
self._x = value
@x.deleter
def x(self):
del self._x
上述代码与 例一 完全等价。注意一定要给附加函数与原始的特征属性相同的名称。
c = C(1)
c.x
1
c.x = 2
c.x
2
del c.x
c.x
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-7-d32ce31f0255> in <module>
1 del c.x
----> 2 c.x
<ipython-input-4-356a299284e7> in x(self)
6 def x(self):
7 """I'm the 'x' property."""
----> 8 return self._x
9
10 @x.setter
AttributeError: 'C' object has no attribute '_x'