相关疑难解决方法(0)

我想了解内置函数的property工作原理.令我困惑的是,property它也可以用作装饰器,但它只在用作内置函数时才需要参数,而不是用作装饰器时.

这个例子来自文档:

class C(object):
    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.")

property的论点是getx,setx,delx和文档字符串.

在下面的代码中property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(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

而且,如何在 …

我很好奇Google Python样式指南中有关属性的建议之一.

在其中,他们给出了以下示例:

class Square(object):
    """A square with two properties: a writable area and a read-only perimeter.

    To use:
    >>> sq = Square(3)
    >>> sq.area
    9
    >>> sq.perimeter
    12
    >>> sq.area = 16
    >>> sq.side
    4
    >>> sq.perimeter
    16
    """

    def __init__(self, side):
         self.side = side

    def __get_area(self):
        """Calculates the 'area' property."""
        return self.side ** 2

    def ___get_area(self):
        """Indirect accessor for 'area' property."""
        return self.__get_area()

    def __set_area(self, area):
        """Sets the 'area' property."""
        self.side = math.sqrt(area)

    def ___set_area(self, area): …

这里是 Python 3，以防万一它很重要。

我试图正确理解如何在@property使用时实现继承，并且我已经搜索了 StackOverflow 并阅读了 20 个类似的问题，但无济于事，因为他们试图解决的问题略有不同。这是我用于测试的代码：

class Example:
    def __init__(self):
        self.__data = None

    @property
    def data(self):
        return self.__data

    @data.setter
    def data(self, data):
        self.__data = data


class Example2(Example):
    def __init__(self):
        super().__init__()

    @property
    def data(self):
        return super().data  # Works!

    @data.setter
    def data(self, data):
        data = '2' + data
        #Example.data = data   # Works, but I want to avoid using the parent name explicitly
        #super().data = data  # Raises AttributeError: 'super' object has no attribute 'data'
        #super().data.fset(self, data) # …

我从有效的Python项目31中获得以下示例：

from weakref import WeakKeyDictionary
class Grade(object):
    def __init__(self):
        self._values = WeakKeyDictionary()
    def __get__(self, instance, instance_type):
        if instance is None: return self
        return self._values.get(instance, 0)

    def __set__(self, instance, value):
        if not (0 <= value <= 100):
            raise ValueError('Grade must be between 0 and 100')
        self._values[instance] = value


# Example 16
class Exam(object):
    math_grade = Grade()
    writing_grade = Grade()
    science_grade = Grade()

first_exam = Exam()
first_exam.writing_grade = 82
second_exam = Exam()
second_exam.writing_grade = 75
print('First ', first_exam.writing_grade, 'is right')
print('Second', second_exam.writing_grade, …