Why does this code keep returning a 'has no attribute' error?

Question

My code is as follows, where sdl2ext.Entity is a third party class.

class Grid(sdl2ext.Entity):
    def __init__(self, world):
        self.w = 3
        self.h = 3
        super(Grid,self).__init__()

    def dump(self):
        print(self.w)

def run():
    world = sdl2ext.World()
    g = Grid(world)
    g.dump()

if __name__ == "__main__":
    run()

The specific error that I get is with the line print(self.w):

AttributeError: object ''Grid'' has no attribute ''w''

Is this something to do with not initialising the underlying base object, sdl2ext.Entity?

Why are you initializing the superclass after setting the private attributes? — Ignacio Vazquez-Abrams, Dec 22 '13 at 23:59
Because of the answer given here: http://stackoverflow.com/questions/10670020/python-class-inheritance-attributeerror-why-how-to-fix . Specifically the definition for the `CastSpell` class given in the accepted answer. — patchwork, Dec 23 '13 at 00:01
You misunderstand. Why are you initializing the superclass *after* setting the private attributes, instead of before? — Ignacio Vazquez-Abrams, Dec 23 '13 at 00:05
@Ignacio, in the accepted answer for that linked question, the superclass is initialised after the private attributes. I thought it was ok to do that. — patchwork, Dec 23 '13 at 00:06
That completely depends on what the superclass does and how it works. — Ignacio Vazquez-Abrams, Dec 23 '13 at 00:23

score 2 · Answer 1 · answered Dec 23 '13 at 00:05

2

You should read the code of the paren class. The class overwrites many special methods, including __getattr__ which likely has something to do with your problem.

answered Dec 23 '13 at 00:05

stefanw

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`__getattr__` is only called as a *fallback*; `self.w` is first looked up in the instance `__dict__`, `__getattr__` is only consulted if it is not found there. – Martijn Pieters Dec 23 '13 at 00:17
1

See the [`__getattr__` documentation](http://docs.python.org/2/reference/datamodel.html#object.__getattr__): *Called when an attribute lookup has not found the attribute in the usual places (i.e. it is not an instance attribute nor is it found in the class tree for `self`)* – Martijn Pieters Dec 23 '13 at 00:26
So @Martijn are you saying that __getattr__ is not the problem? – patchwork Dec 23 '13 at 08:49
@patchwork: I am saying `__getattr__` **cannot** be the problem. – Martijn Pieters Dec 23 '13 at 08:50

Why does this code keep returning a 'has no attribute' error?

1 Answers1