Python property being ignored, acting like an attribute

Question

I've got this RoomPlaceholder class with a distance property; when you set the distance property, it should automatically calculate what the x and y of the class should be, based on a random angle and the distance.

class RoomPlaceholder: def __init__(self, width, height): self.width = width self.height = height self.id = ''.join(random.choice(string.ascii_uppercase + string.digits) for x in range(8)) self.angle = Util.getRandomAngle() # = random.random() * math.pi * 2 self.distance = 0 @property def distance(self): print "gamma" return self._distance @distance.setter def distance(self, value): print "delta" self._distance = value coords = Util.getXYByDist(value, self.angle) # translates angle and distance into integer (x, y) print coords self._x = coords[0] self._y = coords[1] @property def x(self): return self._x @property def y(self): return self._y def __repr__(self): return "%s: [%sx%s] @ (%s, %s) Distance: %s. Angle: %s." % (self.id, self.width, self.height, self.x, self.y, self.distance, self.angle) if __name__ == "__main__": room = RoomPlaceholder(5,5) print "%s\n" % room.distance room.distance = 10 print "%s\n" % room.distance print room pass

However, it's not working. Based on the output from the console, it looks like it's treating distance as an attribute rather than a property; note that I've got print statements in both the getter ("gamma") and setter ("delta") methods, but we never see either in the output when I get or set the distance:

Traceback (most recent call last):0 File "D:\Dropbox\Programming\Python\DungeonGenerator\NewDungeonGenerator.py", line 142, in <module> 10 print room File "D:\Dropbox\Programming\Python\DungeonGenerator\NewDungeonGenerator.py", line 132, in __repr__ return "%s: [%sx%s] @ (%s, %s) Distance: %s. Angle: %s." % (self.id, self.width, self.height, self.x, self.y, self.distance, self.angle) File "D:\Dropbox\Programming\Python\DungeonGenerator\NewDungeonGenerator.py", line 97, in x return self._x AttributeError: RoomPlaceholder instance has no attribute '_x' [Finished in 0.0s]

I'm using Python 2.7, and this is being run via Sublime Text 3 in Windows 7.

jwodder · Accepted Answer · 2013-10-30 21:21:17Z

5

property only works for new-style classes. You need to make RoomPlaceholder a subclass of object by declaring it thusly:

class RoomPlaceholder(object): # etc.

answered Oct 30, 2013 at 21:21

jwodder

58.1k12 gold badges116 silver badges134 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Asmor Over a year ago

I've used properties elsewhere without difficulty, and without using that style of definition. For example, see github.com/Asmor/python-roguelike/blob/master/Level.py#L43 Why would it be working there but not here? EDIT: To clarify, your solution does work; I'm just confused why I haven't run into this problem previously

jwodder Over a year ago

@Asmor: Were you previously working solely in Python 3? In Py3, all classes are new-style, and the (object) bit is redundant, while in Python 2, (object) is needed to get property et alii to work.

Asmor Over a year ago

I did actually start this project in py3, but I've switched to py2. Upon further inspection, that line I mentioned isn't actually working correctly, but its failure wasn't as noticeable. Thanks again!

Collectives™ on Stack Overflow

Python property being ignored, acting like an attribute

1 Answer 1

3 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Linked

Related