Python Attribute error

Question

having problems with this error in python:

File "F:\dykrstra", line 36, in route
while node.label != node.prevNode.label:
AttributeError: 'NoneType' object has no attribute 'label'

Inside this while loop:

 while node.label != node.prevNode.label:
    node = node.prevNode
    labels.append(node.label)

I think it relates to this:

   def __init__(self, label):
        self.label = label
        self.neighbours = []
        self.distances = []
        self.prevNode = None
        self.totalDistance = 0

I'm not sure why prevNode doesn't like the nothing being assigned to it, please help.

It is totally fine that you assign None to prevNode. But the value None has to attributes, so prevNode.label will give you an error. You can try it in the console, type None.label. — Felix Kling
– Felix Kling, Commented Mar 13, 2011 at 16:01

Sven Marnach · Accepted Answer · 2011-03-13 16:01:33Z

6

Your constructor sets self.prevNode to None, and later you try to access node.prevNode.label, which is like trying to access None.label. None doesn't have any attributes, so trying to access any will give you an AttributeError.

answered Mar 13, 2011 at 16:01

Sven Marnach

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Chris Farmiloe · Accepted Answer · 2011-03-13 16:52:57Z

0

As per the other answers (and the error message) you are accessing None.label. If it is expected that node might be None, then you will need to check for it before appending it.

while node.label != node.prevNode.label:
    node = node.prevNode
    if node is not None:
        labels.append(node.label)

answered Mar 13, 2011 at 16:52

Chris Farmiloe

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kenorb · Accepted Answer · 2015-05-23 16:56:48Z

0

Exception AttributeError happens when attribute of the object is not available. An attribute reference is a primary followed by a period and a name.

So basically you need to double check your object and the attribute name.

For example to return a list of valid attributes for that object, use dir():

dir(node)

answered May 23, 2015 at 16:56

kenorb

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