我想了解内置函数属性是如何工作的。让我困惑的是,属性也可以用作装饰器,但它只在用作内置函数时接受参数,而在用作装饰器时不接受参数。

下面的例子来自文档:

class C:
    def __init__(self):
        self._x = None

    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.")

属性的参数是getx, setx, delx和一个doc字符串。

在下面的代码中,属性被用作装饰器。它的对象是x函数,但在上面的代码中,参数中没有对象函数的位置。

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

在本例中,如何创建x.setter和x.deleter装饰器?


当前回答

下面是@property如何实现的一个最小示例:

class Thing:
    def __init__(self, my_word):
        self._word = my_word 
    @property
    def word(self):
        return self._word

>>> print( Thing('ok').word )
'ok'

否则,word仍然是一个方法而不是属性。

class Thing:
    def __init__(self, my_word):
        self._word = my_word
    def word(self):
        return self._word

>>> print( Thing('ok').word() )
'ok'

其他回答

下面是另一个例子:

##
## Python Properties Example
##
class GetterSetterExample( object ):
    ## Set the default value for x ( we reference it using self.x, set a value using self.x = value )
    __x = None


##
## On Class Initialization - do something... if we want..
##
def __init__( self ):
    ## Set a value to __x through the getter / setter... Since __x is defined above, this doesn't need to be set...
    self.x = 1234

    return None


##
## Define x as a property, ie a getter - All getters should have a default value arg, so I added it - it will not be passed in when setting a value, so you need to set the default here so it will be used..
##
@property
def x( self, _default = None ):
    ## I added an optional default value argument as all getters should have this - set it to the default value you want to return...
    _value = ( self.__x, _default )[ self.__x == None ]

    ## Debugging - so you can see the order the calls are made...
    print( '[ Test Class ] Get x = ' + str( _value ) )

    ## Return the value - we are a getter afterall...
    return _value


##
## Define the setter function for x...
##
@x.setter
def x( self, _value = None ):
    ## Debugging - so you can see the order the calls are made...
    print( '[ Test Class ] Set x = ' + str( _value ) )

    ## This is to show the setter function works.... If the value is above 0, set it to a negative value... otherwise keep it as is ( 0 is the only non-negative number, it can't be negative or positive anyway )
    if ( _value > 0 ):
        self.__x = -_value
    else:
        self.__x = _value


##
## Define the deleter function for x...
##
@x.deleter
def x( self ):
    ## Unload the assignment / data for x
    if ( self.__x != None ):
        del self.__x


##
## To String / Output Function for the class - this will show the property value for each property we add...
##
def __str__( self ):
    ## Output the x property data...
    print( '[ x ] ' + str( self.x ) )


    ## Return a new line - technically we should return a string so it can be printed where we want it, instead of printed early if _data = str( C( ) ) is used....
    return '\n'

##
##
##
_test = GetterSetterExample( )
print( _test )

## For some reason the deleter isn't being called...
del _test.x

基本上,与C(对象)的例子相同,除了我使用x代替…我也没有在__init中初始化-…嗯. .我有,但它可以被删除,因为__x被定义为类....的一部分

输出结果为:

[ Test Class ] Set x = 1234
[ Test Class ] Get x = -1234
[ x ] -1234

如果我注释掉自我。在init中X = 1234,那么输出是:

[ Test Class ] Get x = None
[ x ] None

如果我在getter函数中设置_default = None为_default = 0(因为所有getter都应该有一个默认值,但它不是通过我所看到的属性值传递进来的,所以你可以在这里定义它,它实际上并不坏,因为你可以定义默认一次,并在任何地方使用它),即:def x(self, _default = 0):

[ Test Class ] Get x = 0
[ x ] 0

注意:getter逻辑的存在只是为了让值被它操纵,以确保它被它操纵——对于print语句也是如此……

Note: I'm used to Lua and being able to dynamically create 10+ helpers when I call a single function and I made something similar for Python without using properties and it works to a degree, but, even though the functions are being created before being used, there are still issues at times with them being called prior to being created which is strange as it isn't coded that way... I prefer the flexibility of Lua meta-tables and the fact I can use actual setters / getters instead of essentially directly accessing a variable... I do like how quickly some things can be built with Python though - for instance gui programs. although one I am designing may not be possible without a lot of additional libraries - if I code it in AutoHotkey I can directly access the dll calls I need, and the same can be done in Java, C#, C++, and more - maybe I haven't found the right thing yet but for that project I may switch from Python..

注意:在这个论坛的代码输出是坏的-我必须在代码的第一部分添加空格,以使其工作-当复制/粘贴时,确保您将所有空格转换为制表符....我在Python中使用制表符,因为在一个10,000行的文件中,空格的文件大小可以是512KB到1MB,制表符的文件大小可以是100到200KB,这相当于文件大小的巨大差异,并减少了处理时间……

标签也可以调整每个用户-所以如果你喜欢2个空间宽度,4,8或任何你可以做的,这意味着它是周到的开发人员与视力缺陷。

注意:类中定义的所有函数都没有缩进,因为论坛软件中的一个bug -如果复制/粘贴,请确保缩进

文档说它只是创建只读属性的快捷方式。所以

@property
def x(self):
    return self._x

等于

def getx(self):
    return self._x
x = property(getx)

最好的解释在这里: Python @属性解释-如何使用和何时?(例子) 作者:塞尔瓦·普拉巴卡兰|发表于2018年11月5日

它帮助我理解为什么,而不仅仅是如何。

https://www.machinelearningplus.com/python/python-property/

这之后:

class C(object):
    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

等于:

class C(object):
    def __init__(self):
        self._x = None

    def _x_get(self):
        return self._x

    def _x_set(self, value):
        self._x = value

    def _x_del(self):
        del self._x

    x = property(_x_get, _x_set, _x_del, 
                    "I'm the 'x' property.")

等于:

class C(object):
    def __init__(self):
        self._x = None

    def _x_get(self):
        return self._x

    def _x_set(self, value):
        self._x = value

    def _x_del(self):
        del self._x

    x = property(_x_get, doc="I'm the 'x' property.")
    x = x.setter(_x_set)
    x = x.deleter(_x_del)

等于:

class C(object):
    def __init__(self):
        self._x = None

    def _x_get(self):
        return self._x
    x = property(_x_get, doc="I'm the 'x' property.")

    def _x_set(self, value):
        self._x = value
    x = x.setter(_x_set)

    def _x_del(self):
        del self._x
    x = x.deleter(_x_del)

也就是:

class C(object):
    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

这一点已经被很多人澄清了,但这是我一直在寻找的一个直接点。 这是我认为从@property装饰器开始很重要的一点。 如:-

class UtilityMixin():
    @property
    def get_config(self):
        return "This is property"

函数“get_config()”的调用将像这样工作。

util = UtilityMixin()
print(util.get_config)

如果您注意到,我没有使用“()”括号来调用函数。这是我搜索@property装饰器的基本内容。这样你就可以像使用变量一样使用函数。