[Python-Dev] Assignment to None

[Alex Martelli]

The problem is more general: what if a member  (of some external
object we're proxying one way or another) is named print (in Python <
3), or class, or...?  To allow foo.print or bar.class would require
pretty big changes to Python's parser -- I have vague memories that
the issue was discussed ages ago (possibly in conjunction with some
early release of Jython) but never went anywhere much (including
proposals to automatically append an underscore to such IDs in the
proxying layer, etc etc).  Maybe None in particular is enough of a
special case (if it just happens to be hugely often used in dotNET
libraries)?

Alex

On Mon, Jun 9, 2008 at 1:28 AM, Michael Foord <fuzzyman at voidspace.org.uk> wrote:
> Steven D'Aprano wrote:
>>
>> On Mon, 9 Jun 2008 12:24:55 pm Curt Hagenlocher wrote:
>>
>>
>>>
>>> So, it's okay to setattr the attribute name "None" but not okay to set it
>>> directly?
>>
>> I suspect this is off-topic for python-dev, and would be better on
>> comp.lang.python or similar, but for what it's worth, I consider having an
>> attribute named 'None' bad practise, regardless of any runtime checks. But
>> as part of Python's "we're all consenting adults here" philosophy, I
>> wouldn't approve of expensive or extensive run-time checks specifically to
>> prevent it. If you really have to name your attribute None, and are prepared
>> to live with the consequences, then go ahead.
>>
>>
>
> FWIW Curt is asking because he is on the team responsible for implementing
> IronPython.
>
> In .NET you have several enumerations with members called None, for example
> 'Alignment.None'. It would be inconvenient for IronPython users if it
> enforced this particular syntax rule of Python's; that not only is
> assignment to None disallowed but that members named None are invalid
> syntax.
>
> The question is, what is the specification for Python. Is it that assignment
> to None is disallowed and the naming of members called None being invalid
> syntax is merely an artefact of the implementation of this, or does Python
> require this...
>
> Michael Foord
>
>> In a similar fashion:
>>
>>
>>>>>
>>>>> class Parrot(object):
>>>>>
>>
>> ...     pass
>> ...
>>
>>>>>
>>>>> p = Parrot()
>>>>> p.1 = 'spam'
>>>>>
>>
>>  File "<stdin>", line 1
>>    p.1
>>      ^
>> SyntaxError: invalid syntax
>>
>>>>>
>>>>> setattr(p, '1', 'spam')
>>>>>
>>>>>
>>
>>
>>
>
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