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Re: Why no warnings when re-assigning builtin names?

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Date Tue, 16 Aug 2011 16:12:44 +0100
Subject Re: Why no warnings when re-assigning builtin names?
From Chris Angelico <rosuav@gmail.com>
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On Tue, Aug 16, 2011 at 3:13 PM, Philip Semanchuk <philip@semanchuk.com> wrote:
> I am an example. I know enough to turn the theoretical warning on, and I would if I could. I have never shadowed a builtin deliberately. I've done it accidentally plenty of times. There are 84 builtins in my version of Python and I don't have them all memorized. The fact that my editor colors them differently is the only thing I have to back up my leaky memory. Not all editors are so gracious.
>

Rather than "turn a warning on" you can "run your code through a
linting script". There are several excellent ones. Add it to your
makefile or test suite; then you get the testing done over _all_ of
your code, instead of waiting until the moment when you actually
execute it.

> One need look no further than the standard library to see a strong counterexample. grep through the Python source for " file =". I see dozens of examples of this builtin being used as a common variable name. I would call contributors to the standard library above-average coders, and we can see them unintentionally shadowing builtins many times.
>

There are several types of shadowing:

1) Deliberate shadowing because you want to change the behavior of the
name. Extremely rare.
2) Shadowing simply by using the name of an unusual builtin (like
'file') in a context where you never use it. Very common.
3) Unintentional shadowing where you create a variable, but then
intend to use the builtin. This is the only one that's a problem.

list = [...]
is not a problem unless you later on use
foo = list(map(...))
which is more common in Python 3 than Python 2, but fortunately, it'll
throw a nice quick error - nobody's going to use list operations on
the normal 'list' type, nor is anybody going to call an instance of
list.

Definitely a job for linting.

ChrisA

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Re: Why no warnings when re-assigning builtin names? Chris Angelico <rosuav@gmail.com> - 2011-08-15 23:15 +0100
  Re: Why no warnings when re-assigning builtin names? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-16 11:32 +1000
    Re: Why no warnings when re-assigning builtin names? Philip Semanchuk <philip@semanchuk.com> - 2011-08-15 23:23 -0400
      Re: Why no warnings when re-assigning builtin names? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-16 15:15 +1000
        Re: Why no warnings when re-assigning builtin names? Philip Semanchuk <philip@semanchuk.com> - 2011-08-16 10:13 -0400
          Re: Why no warnings when re-assigning builtin names? rantingrick <rantingrick@gmail.com> - 2011-08-16 08:44 -0700
            Re: Why no warnings when re-assigning builtin names? Andrew Berg <bahamutzero8825@gmail.com> - 2011-08-16 12:23 -0500
        Re: Why no warnings when re-assigning builtin names? Chris Angelico <rosuav@gmail.com> - 2011-08-16 16:12 +0100
        Re: Why no warnings when re-assigning builtin names? Ethan Furman <ethan@stoneleaf.us> - 2011-08-16 08:41 -0700
          Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-16 17:11 +0000
            Re: Why no warnings when re-assigning builtin names? Ethan Furman <ethan@stoneleaf.us> - 2011-08-16 10:48 -0700
            Re: Why no warnings when re-assigning builtin names? Tim Chase <python.list@tim.thechases.com> - 2011-08-16 13:34 -0500
        Re: Why no warnings when re-assigning builtin names? Philip Semanchuk <philip@semanchuk.com> - 2011-08-16 11:31 -0400
        Re: Why no warnings when re-assigning builtin names? Philip Semanchuk <philip@semanchuk.com> - 2011-08-16 11:38 -0400
        Re: Why no warnings when re-assigning builtin names? Ethan Furman <ethan@stoneleaf.us> - 2011-08-16 09:19 -0700
          Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-16 17:11 +0000
            Re: Why no warnings when re-assigning builtin names? Ethan Furman <ethan@stoneleaf.us> - 2011-08-16 10:43 -0700
              Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-16 18:56 +0000
                Re: Why no warnings when re-assigning builtin names? Terry Reedy <tjreedy@udel.edu> - 2011-08-16 19:32 -0400
                Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-16 23:49 +0000
                Re: Why no warnings when re-assigning builtin names? Chris Angelico <rosuav@gmail.com> - 2011-08-17 01:02 +0100
                Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-17 01:35 +0000
                Re: Why no warnings when re-assigning builtin names? Chris Angelico <rosuav@gmail.com> - 2011-08-17 08:27 +0100
                Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-17 16:33 +0000
                Re: Why no warnings when re-assigning builtin names? Terry Reedy <tjreedy@udel.edu> - 2011-08-16 22:10 -0400
            Re: Why no warnings when re-assigning builtin names? Chris Angelico <rosuav@gmail.com> - 2011-08-16 19:23 +0100
        Re: Why no warnings when re-assigning builtin names? Tim Chase <python.list@tim.thechases.com> - 2011-08-16 11:10 -0500
        Re: Why no warnings when re-assigning builtin names? Philip Semanchuk <philip@semanchuk.com> - 2011-08-16 12:32 -0400
          Re: Why no warnings when re-assigning builtin names? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-17 11:29 +1000
            Re: Why no warnings when re-assigning builtin names? Philip Semanchuk <philip@semanchuk.com> - 2011-08-16 22:16 -0400
        Re: Why no warnings when re-assigning builtin names? Ethan Furman <ethan@stoneleaf.us> - 2011-08-16 10:07 -0700
        Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-16 17:11 +0000
          Re: Why no warnings when re-assigning builtin names? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-17 10:58 +1000
            Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-17 03:17 +0000
              Re: Why no warnings when re-assigning builtin names? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-17 18:15 +1000
                Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-17 16:33 +0000
                Re: Why no warnings when re-assigning builtin names? Ethan Furman <ethan@stoneleaf.us> - 2011-08-17 10:36 -0700
                Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-17 17:36 +0000
                Re: Why no warnings when re-assigning builtin names? Ethan Furman <ethan@stoneleaf.us> - 2011-08-17 11:13 -0700
                Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-17 18:09 +0000
                Re: Why no warnings when re-assigning builtin names? Chris Angelico <rosuav@gmail.com> - 2011-08-17 18:42 +0100
                Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-17 17:38 +0000
                Re: Why no warnings when re-assigning builtin names? Chris Angelico <rosuav@gmail.com> - 2011-08-17 19:02 +0100
                Re: Why no warnings when re-assigning builtin names? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-18 10:36 +1000
            Re: Why no warnings when re-assigning builtin names? Chris Angelico <rosuav@gmail.com> - 2011-08-17 08:34 +0100
        RE: Why no warnings when re-assigning builtin names? "Gerrat Rickert" <grickert@coldstorage.com> - 2011-08-16 13:15 -0400
        Re: Why no warnings when re-assigning builtin names? Terry Reedy <tjreedy@udel.edu> - 2011-08-16 19:29 -0400
        Re: Why no warnings when re-assigning builtin names? Philip Semanchuk <philip@semanchuk.com> - 2011-08-16 20:18 -0400
        Re: Why no warnings when re-assigning builtin names? Terry Reedy <tjreedy@udel.edu> - 2011-08-16 22:15 -0400
        Re: Why no warnings when re-assigning builtin names? Philip Semanchuk <philip@semanchuk.com> - 2011-08-16 22:51 -0400
        RE: Why no warnings when re-assigning builtin names? "Gerrat Rickert" <grickert@coldstorage.com> - 2011-08-17 09:30 -0400
    Re: Why no warnings when re-assigning builtin names? Chris Angelico <rosuav@gmail.com> - 2011-08-16 09:16 +0100
  Re: Why no warnings when re-assigning builtin names? Chris Torek <nospam@torek.net> - 2011-08-31 21:30 +0000
    Re: Why no warnings when re-assigning builtin names? Seebs <usenet-nospam@seebs.net> - 2011-08-31 21:57 +0000

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