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Re: __bases__ misleading error message

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From Ian Kelly <ian.g.kelly@gmail.com>
Date Sat, 24 Jan 2015 14:45:32 -0700
Subject Re: __bases__ misleading error message
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On Sat, Jan 24, 2015 at 2:14 PM, Mario Figueiredo <marfig@gmail.com> wrote:
> In article <54c39366$0$13006$c3e8da3$5496439d@news.astraweb.com>,
> steve+comp.lang.python@pearwood.info says...
>> >         AttributeError: 'Sub' instance has no attribute '__bases__',
>> >         AttributeError: 'foo' object has no attribute '__bases__'
>>
>> The first would be nice. The second is impossible: objects may have no name,
>> one name, or many names, and they do not know what names they are bound to.
>> So the Sub instance bound to the name 'foo' doesn't know that its name
>> is 'foo', so it cannot display it in the error message.
>
> Thanks for the information! :)
>
> But that begs the OT question:

No, it doesnt. http://en.wikipedia.org/wiki/Begging_the_question

> How does Python maps names to memory
> addresses in the interpreter?

Global variables are looked up in the current stack frame's globals dict.

>>> a = 1
>>> b = 2
>>> globals()['a']
1
>>> globals()['b']
2

Local variables of functions could be handled the same way, but for
efficiency the compiler instead maps the names to indices of a local
variable array associated with the stack frame. Either way, at the C
level the value stored in the dict or array is a pointer to the memory
location of the object.

>     "__main__"
>     from module import a_name
>     y = a_name + 1
>
> How does python interpreter know how to map 'name' to the correct memory
> location, if this __main__ code is only ran after 'module' code?

I'm not sure I'm understanding what you're asking, but the import
statement imports the module, looks up "a_name" in that module's
globals dict, and binds the same object to a_name in the current
module's globals dict.

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Thread

__bases__ misleading error message Mario Figueiredo <marfig@gmail.com> - 2015-01-24 10:16 +0000
  Re: __bases__ misleading error message Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-24 23:43 +1100
    Re: __bases__ misleading error message Mario Figueiredo <marfig@gmail.com> - 2015-01-24 22:14 +0100
      Re: __bases__ misleading error message Ian Kelly <ian.g.kelly@gmail.com> - 2015-01-24 14:45 -0700
        Re: __bases__ misleading error message Mario Figueiredo <marfig@gmail.com> - 2015-01-24 23:09 +0100
          Re: __bases__ misleading error message Chris Angelico <rosuav@gmail.com> - 2015-01-25 09:25 +1100
            Re: __bases__ misleading error message Mario Figueiredo <marfig@gmail.com> - 2015-01-24 23:33 +0100
              Re: __bases__ misleading error message Chris Angelico <rosuav@gmail.com> - 2015-01-25 09:37 +1100
                Re: __bases__ misleading error message Mario Figueiredo <marfig@gmail.com> - 2015-01-24 23:59 +0100
      Re: __bases__ misleading error message Terry Reedy <tjreedy@udel.edu> - 2015-01-24 16:58 -0500
        Re: __bases__ misleading error message Mario Figueiredo <marfig@gmail.com> - 2015-01-24 23:02 +0100
          Re: __bases__ misleading error message Ian Kelly <ian.g.kelly@gmail.com> - 2015-01-24 15:16 -0700
            Re: __bases__ misleading error message Mario Figueiredo <marfig@gmail.com> - 2015-01-24 23:36 +0100
      Re: __bases__ misleading error message Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-25 14:18 +1100
        Re: __bases__ misleading error message Mario Figueiredo <marfig@gmail.com> - 2015-01-25 12:07 +0100
          Re: __bases__ misleading error message Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-25 23:00 +1100
            Re: __bases__ misleading error message Mario Figueiredo <marfig@gmail.com> - 2015-01-25 13:49 +0100
              Re: __bases__ misleading error message Marko Rauhamaa <marko@pacujo.net> - 2015-01-25 14:53 +0200
            Re: __bases__ misleading error message Terry Reedy <tjreedy@udel.edu> - 2015-01-25 16:35 -0500
            Re: __bases__ misleading error message Ian Kelly <ian.g.kelly@gmail.com> - 2015-01-25 19:21 -0700
    Re: __bases__ misleading error message Marco Buttu <marco.buttu@gmail.com> - 2015-01-24 23:09 +0100
    Re: __bases__ misleading error message Marco Buttu <marco.buttu@gmail.com> - 2015-01-24 15:12 +0100
  Re: __bases__ misleading error message Terry Reedy <tjreedy@udel.edu> - 2015-01-24 14:24 -0500
    Re: __bases__ misleading error message Mario Figueiredo <marfig@gmail.com> - 2015-01-24 22:03 +0100
    Re: __bases__ misleading error message Marco Buttu <marco.buttu@gmail.com> - 2015-01-24 22:51 +0100
      Re: __bases__ misleading error message Terry Reedy <tjreedy@udel.edu> - 2015-01-24 19:55 -0500
        Re: __bases__ misleading error message Marco Buttu <marco.buttu@gmail.com> - 2015-01-25 11:30 +0100
    Re: __bases__ misleading error message Marco Buttu <marco.buttu@gmail.com> - 2015-01-24 22:51 +0100

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