[Python-Dev] Assignment to None (original) (raw)

Michael Foord fuzzyman at voidspace.org.uk
Mon Jun 9 10:28:03 CEST 2008

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 "", line 1 p.1 ^ SyntaxError: invalid syntax setattr(p, '1', 'spam')

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