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

"Martin v. Löwis" martin at v.loewis.de
Mon Jun 9 22:36:05 CEST 2008

At the global level, the subversion does not work:

I think you are misinterpreting what you are seeing. When you refer to the global identifier None, the compiler just knows that it must be the NoneType singleton, and returns it as a constant, without doing any name lookup. So it isn't that assignment of the global None fails to be performed; instead, the compiler just ignores any global with the name None that might have been set.

The compiler doesn't do the same thing for attributes, and rightfully so: it would surely be surprising if foo.None would yield the NoneType singleton for any arbitrary foo. Instead, the compiler generates a regular attribute, which then regularly finds the attribute in the object's dictionary if it is there.

I was a little surprised by this. ISTM that f.None should consistently work or not work both for getting and setting.

That will only happen when (if) None becomes a keywords: then foo.None will be a syntax error. You will still be able to put attributes named 'None' (or 'import' or 'if') into any object using getattr/setattr, or by direct access to dict.

Regards, Martin

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