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Re: Scope of variable inside list comprehensions?

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On Tue, Dec 6, 2011 at 9:57 AM, Roy Smith <roy@panix.com> wrote:
> I may be in the minority here, but it doesn't bother me much that my use of 'id' shadows a built-in.  Especially in small scopes like this, I use whatever variable names make the the code easiest to read and don't worry about shadowing builtins.  I don't have an exhaustive list of builtins in my head, so even if I worried about common ones like file or id, I'm sure I'd miss some others.  So I don't sweat it.
>
> If shadowing builtins was really evil, they'd be reserved keywords and then you wouldn't be able to do it.

Agreed. The name 'id' is one that's shadowed benignly in a lot of
code. In the context of the original question, it's not an issue -
there'll be no confusion.

Python's scoping rules are "do what the programmer probably wants".
This works most of the time, but occasionally you get edge cases where
things are a bit weird, and C-style explicit scoping (with infinitely
nested block scope) begins to look better. But for probably 99% of
situations, Python's system "just works".

If you need more flexibility in the exception you throw, it may be
worth putting together a filter:

def HttpSongId(id):
   try:
       return Song.get(int(id))
   except Song.DoesNotExist:
       return HttpResponseBadRequest("unknown song id (%d)" % id)

   song_ids = request.POST.getlist('song_id')
   songs = [HttpSongId(id) for id in song_ids]

This encapsulates things in a somewhat weird way, but if there's any
other work to be done at the same time, you could probably come up
with a better name for the exception filter function.

ChrisA

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Thread

Scope of variable inside list comprehensions? Roy Smith <roy@panix.com> - 2011-12-05 09:04 -0800
  Re: Scope of variable inside list comprehensions? Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-12-05 20:04 +0200
  Re: Scope of variable inside list comprehensions? Peter Otten <__peter__@web.de> - 2011-12-05 19:10 +0100
  Re: Scope of variable inside list comprehensions? Jean-Michel Pichavant <jeanmichel@sequans.com> - 2011-12-05 19:57 +0100
    Re: Scope of variable inside list comprehensions? Roy Smith <roy@panix.com> - 2011-12-05 11:15 -0800
    Re: Scope of variable inside list comprehensions? Roy Smith <roy@panix.com> - 2011-12-05 11:15 -0800
      Re: Scope of variable inside list comprehensions? Terry Reedy <tjreedy@udel.edu> - 2011-12-05 15:22 -0500
        Re: Scope of variable inside list comprehensions? Roy Smith <roy@panix.com> - 2011-12-05 14:36 -0800
        Re: Scope of variable inside list comprehensions? Roy Smith <roy@panix.com> - 2011-12-05 14:36 -0800
          Re: Scope of variable inside list comprehensions? Terry Reedy <tjreedy@udel.edu> - 2011-12-05 21:23 -0500
    Re: Scope of variable inside list comprehensions? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-05 22:35 +0000
      Re: Scope of variable inside list comprehensions? Roy Smith <roy@panix.com> - 2011-12-05 14:57 -0800
        Re: Scope of variable inside list comprehensions? Chris Angelico <rosuav@gmail.com> - 2011-12-06 13:35 +1100
      Re: Scope of variable inside list comprehensions? Jean-Michel Pichavant <jeanmichel@sequans.com> - 2011-12-06 11:38 +0100
  Re: Scope of variable inside list comprehensions? Rainer Grimm <r.grimm@science-computing.de> - 2011-12-05 22:42 -0800
    Re: Scope of variable inside list comprehensions? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-06 02:16 -0800

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