为什么尝试通过 Python 属性设置 "points" 会导致无限递归？

Question

为什么尝试通过 Python 属性设置“点”会导致无限递归？

使用Python 3

import Task

myTask = Task.Task("Test",-5)

myTask.points = -7

print(myTask)

class Task:

def __init__(self,name="",points=0,times_done=0):
    self.name = name
    self.points = points
    self.times_done = times_done

@property
def points(self):
    return self.points

@points.setter
def points(self, points):
    if (points < 0):
        self.points = 0
    else:
        self.points = points

def __str__(self):
    return "The task '" + self.name + "' is worth " + str(self.points) + " and has been completed " + str(self.times_done) + " times."

当它尝试用值 -5 构造它时（应通过属性将其设置为 0），它会在 setter 中的行 self.points = points 上无限递归 function/decoration @points.setter.

谢谢！

Answer 1

因为self.points = ...调用了setter；在 setter 中，执行 self.points = ... 调用 setter；递归重复直到堆栈溢出。

通过使用其他名称，您可以防止递归：例如self._points。

或者不使用 self.points = ...，而是使用 self.__dict__['points'] = ..（与 getter 相同）：

@property
def points(self):
    return self.__dict__['points']

@points.setter
def points(self, points):
    if points < 0:
        self.__dict__['points'] = 0
    else:
        self.__dict__['points'] = points
    # self.__dict__['points'] = max(0, points)

Answer 2

那是因为在你的 property setter 里面，它再次调用自己：

@points.setter
def points(self, points):
    if (points < 0):
        self.points = 0 # call itself again here
    else:
        self.points = points # call itself again here

使用property时需要另外一个字段来存储实际值，最好是"private" field:

class Task(object):
    def __init__(self,name="",points=0,times_done=0):
            self.name = name
            self.points = points
            self.times_done = times_done

    @property
    def points(self):
            return self._points

    @points.setter
    def points(self, points):
            if (points < 0):
                    self._points = 0
            else:
                    self._points = points

为什么尝试通过 Python 属性设置 "points" 会导致无限递归？

Why does trying to set "points" via Python properties cause infinite recursion?

python

recursion

decorator

getter-setter

python-3.x