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Re: Test None for an object that does not implement ==

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Date Mon, 26 Dec 2011 01:04:06 +1100
Subject Re: Test None for an object that does not implement ==
From Chris Angelico <rosuav@gmail.com>
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On Mon, Dec 26, 2011 at 12:48 AM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> I can't think of any other un-subclassable classes other than NoneType.
> Which ones are you thinking of?

I don't remember, but it was mentioned in a thread a little while ago.
Experimentation shows that 'bool' is one of them, though. This may
shed some light:

>>> class Foo(type(iter)):
	pass

Traceback (most recent call last):
  File "<pyshell#103>", line 1, in <module>
    class Foo(type(iter)):
TypeError: type 'builtin_function_or_method' is not an acceptable base type

I think there are certain types that are actually not implemented as
classes, and hence cannot be subclassed. This is almost certainly an
implementation detail though; my testing was done in Py3.2 (on Windows
fwiw).

ChrisA

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Thread

Test None for an object that does not implement == GZ <zyzhu2000@gmail.com> - 2011-12-24 23:09 -0800
  Re: Test None for an object that does not implement == Paul Rubin <no.email@nospam.invalid> - 2011-12-24 23:28 -0800
  Re: Test None for an object that does not implement == Nobody <nobody@nowhere.com> - 2011-12-25 09:38 +0000
    Re: Test None for an object that does not implement == Lie Ryan <lie.1296@gmail.com> - 2011-12-25 22:10 +1100
      Re: Test None for an object that does not implement == Roy Smith <roy@panix.com> - 2011-12-25 08:17 -0500
        Re: Test None for an object that does not implement == Chris Angelico <rosuav@gmail.com> - 2011-12-26 00:35 +1100
          Re: Test None for an object that does not implement == Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-25 13:48 +0000
            Re: Test None for an object that does not implement == Chris Angelico <rosuav@gmail.com> - 2011-12-26 01:04 +1100
            Re: Test None for an object that does not implement == Christian Heimes <lists@cheimes.de> - 2011-12-26 01:37 +0100
          Re: Test None for an object that does not implement == Roy Smith <roy@panix.com> - 2011-12-25 09:13 -0500
            Re: Test None for an object that does not implement == Chris Angelico <rosuav@gmail.com> - 2011-12-26 01:23 +1100
            Re: Test None for an object that does not implement == Lie Ryan <lie.1296@gmail.com> - 2011-12-26 04:13 +1100
    Re: Test None for an object that does not implement == Ian Kelly <ian.g.kelly@gmail.com> - 2011-12-25 19:02 -0700
    Re: Test None for an object that does not implement == Ethan Furman <ethan@stoneleaf.us> - 2011-12-25 20:26 -0800
  Re: Test None for an object that does not implement == Larry Hudson <orgnut@yahoo.com> - 2011-12-25 15:45 -0800
    Re: Test None for an object that does not implement == Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-12-25 19:06 -0500
      Re: Test None for an object that does not implement == Roy Smith <roy@panix.com> - 2011-12-25 19:27 -0500
        Re: Test None for an object that does not implement == Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-12-25 19:58 -0500
    Re: Test None for an object that does not implement == Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-26 00:52 +0000
  Re: Test None for an object that does not implement == Ethan Furman <ethan@stoneleaf.us> - 2011-12-25 20:27 -0800
  Re: Test None for an object that does not implement == Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-12-26 00:22 -0500
    Re: Test None for an object that does not implement == Roy Smith <roy@panix.com> - 2011-12-26 08:43 -0500
  Re: Test None for an object that does not implement == Paul Rudin <paul.nospam@rudin.co.uk> - 2011-12-26 14:33 +0000
  Re: Test None for an object that does not implement == Ethan Furman <ethan@stoneleaf.us> - 2011-12-26 09:14 -0800

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