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Closure/method definition question for Python 2.7

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  Closure/method definition question for Python 2.7 "Brunick, Gerard:(Constellation)" <Gerard.Brunick@constellation.com> - 2014-03-10 17:27 +0000
    Re: Closure/method definition question for Python 2.7 Marko Rauhamaa <marko@pacujo.net> - 2014-03-10 19:36 +0200
      Re: Closure/method definition question for Python 2.7 Neil Cerutti <neilc@norwich.edu> - 2014-03-11 13:20 +0000

#68165 — Closure/method definition question for Python 2.7

The following code:

---
class Test(object):
    x = 10

    def __init__(self):
        self.y = x

t = 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 in 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.  For example, the following is fine (if nonsensical):

---
def outer():
    x = 10

    def __init__(self):
        self.y = x

    return __init__

t = outer()
print t
---

Can anyone explain this behavior?  It is clear that you could simply use self.x to access the variable x inside of __init__, but this isn't really the point of the question.  

Thanks in advance,
Gerard

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#68167

"Brunick, Gerard:(Constellation)" <Gerard.Brunick@constellation.com>:

> class Test(object):
>     x = 10
>
>     def __init__(self):
>         self.y = x
>
> t = Test()
> ---
>
> raises
>
> NameError: global name 'x' is not defined.

In the snippet, x is neither local to __init__() nor global to the
module. It is in the class scope. You can refer to it in one of two
ways:

   Test.x

or:

   self.x


Marko

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#68216

On 2014-03-10, Marko Rauhamaa <marko@pacujo.net> wrote:
> "Brunick, Gerard:(Constellation)" <Gerard.Brunick@constellation.com>:
>
>> class Test(object):
>>     x = 10
>>
>>     def __init__(self):
>>         self.y = x
>>
>> t = Test()
>> ---
>>
>> raises
>>
>> NameError: global name 'x' is not defined.
>
> In the snippet, x is neither local to __init__() nor global to
> the module. It is in the class scope. You can refer to it in
> one of two ways:
>
>    Test.x
>
> or:
>
>    self.x

The latter will work only to read the class variable. If you
assign to self.x you'll create a new instance variable that hides
the class variable.

-- 
Neil Cerutti

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