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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Mon, 10 Mar 2014 18:26:27 -0600
Subject: Re: Closure/method definition question for Python 2.7
To: Python <python-list@python.org>
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On Mon, Mar 10, 2014 at 11:27 AM, Brunick, Gerard:(Constellation)
<Gerard.Brunick@constellation.com> wrote:
> The following code:
>
> ---
> class Test(object):
>     x =3D 10
>
>     def __init__(self):
>         self.y =3D x
>
> t =3D Test()
> ---
>
> raises
>
> NameError: global name 'x' is not defined.
>
> in Python 2.7.  I don't understand why.  I would assume that when __init_=
_ is being defined, it is just a regular old function and x is a variable i=
n an outer scope, so the function __init__ would close over the variable x.=
  Moreover, the variable x is not being modified, so this should be O.K.  F=
or example, the following is fine (if nonsensical):

Class scopes and function scopes are not equivalent; class attributes
are not considered for closures.  Only local variables of outer
functions are considered.  At the time __init__ is defined the Test
class has not been created yet, and so the variable x is in local
scope then, e.g.:

    class Test(object):
        x =3D 10

        def __init__(self, y=3Dx):
            self.y =3D y

This works fine, because the x is evaluated when the function is
created, while it's still in local scope.  But Python won't create a
closure for it.