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Groups > comp.lang.python > #10458

NoneType and new instances

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Consider:

Python 3.2 (r32:88445, Feb 20 2011, 21:29:02) [MSC v.1500 32 bit 
(Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
--> for ins in ({0:'0'}, (1,), set([2, 3]), [4, 5], 6, 'seven',
... 8.0, True, None):
...   print(type(ins))
...   type(ins)()
...
<class 'dict'>
{}
<class 'tuple'>
()
<class 'set'>
set()
<class 'list'>
[]
<class 'int'>
0
<class 'str'>
''
<class 'float'>
0.0
<class 'bool'>
False
<class 'NoneType'>
Traceback (most recent call last):
   File "<stdin>", line 3, in <module>
TypeError: cannot create 'NoneType' instances

Why is NoneType unable to produce a None instance?  I realise that None 
is a singleton, but so are True and False, and bool is able to handle 
returning them:

--> bool(0) is bool(0)
True

This feels like a violation of 'Special cases aren't special enough to 
break the rules.'

~Ethan~

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Thread

NoneType and new instances Ethan Furman <ethan@stoneleaf.us> - 2011-07-28 08:39 -0700
  Re: NoneType and new instances Billy Mays <81282ed9a88799d21e77957df2d84bd6514d9af6@myhashismyemail.com> - 2011-07-28 11:34 -0400
  Re: NoneType and new instances Ben Finney <ben+python@benfinney.id.au> - 2011-07-29 07:46 +1000
    Re: NoneType and new instances Ethan Furman <ethan@stoneleaf.us> - 2011-07-28 15:26 -0700
      Re: NoneType and new instances Ben Finney <ben+python@benfinney.id.au> - 2011-07-29 09:52 +1000
  Re: NoneType and new instances Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-07-29 11:16 +1000
    Re: NoneType and new instances Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-07-30 14:50 +1200
      Re: NoneType and new instances Terry Reedy <tjreedy@udel.edu> - 2011-07-30 09:35 -0400
      Re: NoneType and new instances python@bdurham.com - 2011-07-30 11:43 -0400
  Re: NoneType and new instances "bruno.desthuilliers@gmail.com" <bruno.desthuilliers@gmail.com> - 2011-07-30 09:39 -0700
    Re: NoneType and new instances Terry Reedy <tjreedy@udel.edu> - 2011-07-30 23:34 -0400
      Re: NoneType and new instances Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-07-31 14:28 +1000

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