筆記-python-語法-property
筆記-python-語法-property
1. property
看到@property，不明白什麽意思，查找文檔了解一下。
1.1. property類
proerty是python自帶的類，在
>>> property
<class ‘property‘>
>>> 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‘]
>>> property.__class__
<class ‘type‘>
官方文檔：
class property(fget=None, fset=None, fdel=None, doc=None)
Return a property attribute.
fget是一個獲取屬性值的函數，fset是設定值的函數，fdel是刪除值的函數。doc創建屬性的說明文檔。
案例：
class C:
def __init__(self):
self._x = None
def getx(self):
return
def setx(self, value):
self._x = value
def delx(self):
del self._x
x = property(getx, setx, delx, "I‘m the ‘x‘ property.")
運行結果如下：
>>> C.x
<property object at 0x000000BC05B078B8>
>>> dir(C)
[‘__class__‘, ‘__delattr__‘, ‘__dict__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__gt__‘, ‘__hash__‘, ‘__init__‘, ‘__init_subclass__‘, ‘__le__‘, ‘__lt__‘, ‘__module__‘, ‘__ne__‘, ‘__new__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘, ‘__setattr__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘__weakref__‘, ‘delx‘, ‘getx‘, ‘setx‘, ‘x‘]
解釋：上面的代碼給類C添加了一個屬性x，而x是一個property對象，這樣做的結果是可以像下面這樣操作self._x
>>> a = C()
賦值
>>> a.x = 6
>>> a._x #6
刪除
>>> del(a.x)
>>> a.x
Traceback (most recent call last):
File "<pyshell#27>", line 1, in <module>
a.x
File "E:\python\person_code\interview questions\built-in.py", line 47, in getx
return self._x
AttributeError: ‘C‘ object has no attribute ‘_x‘
>>> a._x
Traceback (most recent call last):
File "<pyshell#28>", line 1, in <module>
a._x
AttributeError: ‘C‘ object has no attribute ‘_x‘
最終的結果就是簡化了實例對象屬性的操作代碼。
再看下面的代碼：
A property object has getter, setter, and deleter methods usable as decorators that create a copy of the property with the corresponding accessor function set to the decorated function.
This is best explained with an example:
class C:
def __init__(self):
self._x = None
@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
這裏使用的裝飾符實現，功能與上例沒什麽區別，但代碼更簡潔。
註意seter和deleter並不是必需的。
怎麽實現的就不討論了，總而言之它可以簡化實例屬性操作，簡化代碼。
筆記-python-語法-property