Why does trying to set "points" using Python properties cause infinite recursion?
Why does trying to set "points" through Python properties cause infinite recursion?
Using 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."
When it tries to plot it with a value of -5 (which should set it to 0, via a property), it recurses infinitely on the line self.points = points
in the setter / tec function@points.setter.
Thank!
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Because the self.points = ...
call to setter; inside the setter self.points = ...
, the calling device is called; recursion is repeated until.
By using a different name, you can prevent recursion: self._points
eg.
Or self.points = ...
use instead self.__dict__['points'] = ..
(same for getter):
@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)
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This is because inside yours property setter
it calls itself again:
@points.setter
def points(self, points):
if (points < 0):
self.points = 0 # call itself again here
else:
self.points = points # call itself again here
You need a different field to store the actual value when used property
, and it would be better to be "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
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