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Re: anomaly

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Date Tue, 12 May 2015 00:13:00 +1000
Subject Re: anomaly
From Chris Angelico <rosuav@gmail.com>
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On Mon, May 11, 2015 at 11:38 PM, Antoon Pardon
<antoon.pardon@rece.vub.ac.be> wrote:
> "We allow buitins to be overridden", doesn't sound as a very accurate
> description of the underlining reason, when you know that things have
> been removed from builtins and made a keyword in order to prevent them
> from being overridden.

There are principles, and then there are specific instances that go
against those principles. The overarching principle has its
justification; the violations have to have their own justifications.
As Steven said, there are no a priori reasons for most things - or to
put it another way, there are very few design decisions that come down
to a fundamental "this is right, this is wrong" - but there can be
strong and weak justifications for things.

Why does Python have most built-ins as simply looked-up names that can
be overridden? Because otherwise, there would be a veritable ton of
keywords:

>>> dir(builtins)
['ArithmeticError', 'AssertionError', 'AttributeError',
'BaseException', 'BlockingIOError', 'BrokenPipeError', 'BufferError',
'BytesWarning', 'ChildProcessError', 'ConnectionAbortedError',
'ConnectionError', 'ConnectionRefusedError', 'ConnectionResetError',
'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError',
'Exception', 'False', 'FileExistsError', 'FileNotFoundError',
'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError',
'ImportError', 'ImportWarning', 'IndentationError', 'IndexError',
'InterruptedError', 'IsADirectoryError', 'KeyError',
'KeyboardInterrupt', 'LookupError', 'MemoryError', 'NameError',
'None', 'NotADirectoryError', 'NotImplemented', 'NotImplementedError',
'OSError', 'OverflowError', 'PendingDeprecationWarning',
'PermissionError', 'ProcessLookupError', 'ReferenceError',
'ResourceWarning', 'RuntimeError', 'RuntimeWarning', 'StopIteration',
'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit',
'TabError', 'TimeoutError', 'True', 'TypeError', 'UnboundLocalError',
'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError',
'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning',
'ValueError', 'Warning', 'ZeroDivisionError', '__build_class__',
'__debug__', '__doc__', '__import__', '__loader__', '__name__',
'__package__', '__spec__', 'abs', 'all', 'any', 'ascii', 'bin',
'bool', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod',
'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict',
'dir', 'divmod', 'enumerate', 'eval', 'exec', 'exit', 'filter',
'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr',
'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance',
'issubclass', 'iter', 'len', 'license', 'list', 'locals', 'map',
'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord',
'pow', 'print', 'property', 'quit', 'range', 'repr', 'reversed',
'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str',
'sum', 'super', 'tuple', 'type', 'vars', 'zip']

in addition to these, which _are_ keywords:

>>> keyword.kwlist
['False', 'None', 'True', 'and', 'as', 'assert', 'break', 'class',
'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for',
'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal',
'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with',
'yield']

Python 2 had 'print' as a keyword, and it was specifically turned into
a non-keyword in Python 3 to allow it to be overridden. It could have
been turned into a function while still being a keyword, but it
wasn't. Conversely, True and False became keywords, because there's no
practical reason to override them. [1] You may well want to shadow
'copyright' with your own program's copyright notice, given that the
built-in name is primarily there for interactive use. You might use
'input' to store the incoming text in a non-interactive program, or
'quit' in an interactive one to store a flag that becomes True when
the user wants to terminate. Very frequently, 'id' is used as a
database ID. None of these shadowings is a problem to the language;
chances are none of them will ever be a problem to your code either.
Having most of the built-in names *not* be keywords means that adding
new built-ins doesn't break code; code that used the name for some
other meaning will still work, but won't be able to use the new
feature. That's a good thing.

ChrisA

[1] http://thedailywtf.com/articles/What_Is_Truth_0x3f_ notwithstanding.

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Re: anomaly Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-10 10:42 -0600
  Re: anomaly Rustom Mody <rustompmody@gmail.com> - 2015-05-10 09:48 -0700
    Re: anomaly Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-10 18:21 +0100
    Re: anomaly Gary Herron <gherron@digipen.edu> - 2015-05-10 10:28 -0700
      Re: anomaly Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-11 13:19 +1000
    Re: anomaly boB Stepp <robertvstepp@gmail.com> - 2015-05-10 14:12 -0500
      Re: anomaly Mel Wilson <mwilson@the-wire.com> - 2015-05-11 13:37 +0000
        Re: anomaly Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-12 02:35 +1000
          Re: anomaly Mel Wilson <mwilson@the-wire.com> - 2015-05-11 20:48 +0000
            Re: anomaly Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-12 12:18 +1000
    Re: anomaly Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-11 08:40 +0100
    Re: anomaly Chris Angelico <rosuav@gmail.com> - 2015-05-11 17:44 +1000
    Re: anomaly Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-05-11 12:15 +0200
      Re: anomaly John Ladasky <john_ladasky@sbcglobal.net> - 2015-05-12 17:47 -0700
        Re: anomaly Rustom Mody <rustompmody@gmail.com> - 2015-05-12 17:56 -0700
          Re: anomaly Paul Rubin <no.email@nospam.invalid> - 2015-05-12 19:16 -0700
            Re: anomaly Rustom Mody <rustompmody@gmail.com> - 2015-05-12 19:31 -0700
    Re: anomaly Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-11 11:40 +0100
    Re: anomaly Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-05-11 13:39 +0200
      Re: anomaly Marko Rauhamaa <marko@pacujo.net> - 2015-05-11 14:58 +0300
        Re: anomaly Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-05-11 15:27 +0200
          Re: anomaly Marko Rauhamaa <marko@pacujo.net> - 2015-05-11 17:03 +0300
            Re: anomaly zipher <dreamingforward@gmail.com> - 2015-05-11 07:56 -0700
              Re: anomaly Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-05-11 20:32 -0400
            Re: anomaly Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-05-12 13:34 +0200
          Re: anomaly Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-12 01:44 +1000
            Re: anomaly zipher <dreamingforward@gmail.com> - 2015-05-11 09:17 -0700
            Re: anomaly Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-05-11 20:33 -0400
            Re: anomaly Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-05-12 14:31 +0200
      Re: anomaly Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-11 22:34 +1000
        Re: anomaly Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-05-11 15:38 +0200
        Re: anomaly Chris Angelico <rosuav@gmail.com> - 2015-05-12 00:13 +1000
        Re: anomaly Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-05-12 17:37 +1200
        Re: anomaly Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-05-12 13:55 +0200
          Re: anomaly Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-12 23:56 +1000
            Re: anomaly zipher <dreamingforward@gmail.com> - 2015-05-12 08:34 -0700
              Re: anomaly Chris Angelico <rosuav@gmail.com> - 2015-05-13 01:43 +1000
                Re: anomaly zipher <dreamingforward@gmail.com> - 2015-05-12 20:39 -0700
              Re: anomaly Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-12 17:19 +0100
                Re: anomaly zipher <dreamingforward@gmail.com> - 2015-05-13 08:19 -0700
              Re: anomaly Skip Montanaro <skip.montanaro@gmail.com> - 2015-05-12 11:22 -0500
                Re: anomaly Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-13 13:58 +1000
              Re: anomaly Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-12 12:07 -0600
            Re: anomaly Terry Reedy <tjreedy@udel.edu> - 2015-05-12 16:23 -0400
            Re: anomaly Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-05-13 09:07 +0200
          Re: anomaly Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-05-13 12:19 +1200
            Re: anomaly Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-05-13 09:23 +0200
        Re: anomaly Gary Herron <gherron@digipen.edu> - 2015-05-12 09:07 -0700
    Re: anomaly Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-11 12:47 +0100
    Re: anomaly boB Stepp <robertvstepp@gmail.com> - 2015-05-11 07:43 -0500
    Re: anomaly boB Stepp <robertvstepp@gmail.com> - 2015-05-11 07:26 -0500
  Re: anomaly zipher <dreamingforward@gmail.com> - 2015-05-10 17:48 -0700
    Re: anomaly Gary Herron <gherron@digipen.edu> - 2015-05-10 18:07 -0700
      Re: anomaly zipher <dreamingforward@gmail.com> - 2015-05-10 18:18 -0700
        Re: anomaly Chris Angelico <rosuav@gmail.com> - 2015-05-11 11:53 +1000
          Re: anomaly zipher <dreamingforward@gmail.com> - 2015-05-10 19:09 -0700
          Re: anomaly Rustom Mody <rustompmody@gmail.com> - 2015-05-10 19:12 -0700
            Re: anomaly Chris Angelico <rosuav@gmail.com> - 2015-05-11 12:20 +1000
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