以下来自 What’s the pythonic way to use getters and setters?
简要用法
class C(object):
def __init__(self):
self._x = None
@property
def x(self):
"""I'm the 'x' property."""
print("getter of x called")
return self._x
@x.setter
def x(self, value):
print("setter of x called")
self._x = value
@x.deleter
def x(self):
print("deleter of x called")
del self._x
c = C()
c.x = 'foo' # setter called
foo = c.x # getter called
del c.x # deleter called
其他解释
在 Python 中，不要使用”getters” and “setters”，而是要用属性，即attributes
这个东西的背后需求是什么？
假设用户已经这么用了：
value = 'something'
obj.attribute = value
value = obj.attribute
del obj.attribute
上面的用法就是很普通的啦，就是public 的属性啦。
假设我们现在突然需要改变 setting and getting，同时不需要改变用户代码，那么这个时候就可以使用 property decorator来实现啦：
class Obj:
"""property demo"""
#
@property
def attribute(self): # implements the get - this name is *the* name
return self._attribute
#
@attribute.setter
def attribute(self, value): # name must be the same
self._attribute = value
#
@attribute.deleter
def attribute(self): # again, name must be the same
del self._attribute
此时，如下的老代码依然可用：
obj = Obj()
obj.attribute = value
the_value = obj.attribute
del obj.attribute
很显然，这么搞之后，我们就可以对class的普通属性施加更多的限制，例如进行 range check，因此具有更大的自由度。
例如：
class Protective(object):
def __init__(self, start_protected_value=0):
self.protected_value = start_protected_value
@property
def protected_value(self):
return self._protected_value
@protected_value.setter
def protected_value(self, value):
if value != int(value):
raise TypeError("protected_value must be an integer")
if 0 <= value <= 100:
self._protected_value = int(value)
else:
raise ValueError("protected_value must be " +
"between 0 and 100 inclusive")
@protected_value.deleter
def protected_value(self):
raise AttributeError("do not delete, protected_value can be set to 0")
结论
一开始用简单的属性就行了，假如以后对该属性的setting, getting, and deleting有更多限制的话，再用property decorator
Start with simple attributes.
If you later need functionality around the setting, getting, and deleting, you can add it with the property decorator.
Avoid functions named set_… and get_… - that’s what properties are for.