[Python-ideas] Crazy idea: allow keywords as names in certain positions

Nathan Schneider neatnate at gmail.com
Sun May 13 15:01:54 EDT 2018

Care would have to be taken in the grammar to avoid syntactic ambiguity.
For example:

x = 1
def not(x):

if not - x: # Is this 'not' the keyword or the identifier? not (-x), or not
minus x?


On Sun, May 13, 2018 at 2:20 PM Guido van Rossum <guido at python.org> wrote:

> As anyone still following the inline assignment discussion knows, a
> problem with designing new syntax is that it's hard to introduce new
> keywords into the language, since all the nice words seem to be used as
> method names in popular packages. (E.g. we can't use 'where' because
> there's numpy.where
> <https://docs.scipy.org/doc/numpy-1.14.0/reference/generated/numpy.where.html>,
> and we can't use 'given' because it's used in Hypothesis
> <http://hypothesis.readthedocs.io/en/latest/quickstart.html>.)
> The idea I had (not for the first time :-) is that in many syntactic
> positions we could just treat keywords as names, and that would free up
> these keywords.
> For example, we could allow keywords after 'def' and after a period, and
> then the following would become legal:
> class C:
>     def and(self, other):
>         return ...
> a = C()
> b = C()
> print(a.and(b))
> This does not create syntactic ambiguities because after 'def' and after a
> period the grammar *always* requires a NAME.
> There are other positions where we could perhaps allow this, e.g. in a
> decorator, immediately after '@' (the only keyword that's *syntactically*
> legal here is 'not', though I'm not sure it would ever be useful).
> Of course this would still not help for names of functions that might be
> imported directly (do people write 'from numpy import where'?). And it
> would probably cause certain typos be harder to diagnose.
> I should also mention that this was inspired from some messages where Tim
> Peters berated the fashion of using "reserved words", waxing nostalgically
> about the old days of Fortran (sorry, FORTRAN), which doesn't (didn't?)
> have reserved words at all (nor significant whitespace, apart from the
> "start in column 7" rule).
> Anyway, just throwing this out. Please tear it apart!
> --
> --Guido van Rossum (python.org/~guido)
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