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

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Date Tue, 16 Aug 2011 11:10:46 -0500
From Tim Chase <python.list@tim.thechases.com>
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Subject Re: Why no warnings when re-assigning builtin names?
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On 08/16/2011 10:31 AM, Philip Semanchuk wrote:
> On Aug 16, 2011, at 11:12 AM, Chris Angelico wrote:
>> 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.
>
> Yes, but before you get to #3 you have to go through #2. The
> way I see it, #2 is setting a trap, #3 is actually stepping
> in it. I don't want to do either. Neither do I like working
> with code that has set trap #2 for me.

Chris succinctly described the times I've done shadowing. 
Fortunately, the shadowing done in #3 (which you appropriately 
describe as being a superset of #2) is fairly remedied with most 
editors...since it usually occurs when you have "oh, I 
accidentally shadowed builtin X", so you just do a global 
search-and-replace for all those places you shadowed X and rename 
it to something like "my_X" and proceed to use X as the builtin.

The bigger issue I have is module shadowing which is trickier to 
catch and produces weird symptoms (i.e. cryptic errors).  The 
most common one I see is creating a local module called 
"email.py" and then having issues when trying to use 
standard-library email calls which find your local email.py 
before they find the email.py file in the standard library.  I 
actually wrote a tool to scan for duplicate modules in 
$PYTHONPATH (pretty dumb tool, could easily have broken on things 
like zipfile imports, DLLs, etc), but it made diagnosing the 
issue easier.

-tkc

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Thread

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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