[Python-ideas] Make keywords KEYwords only in places they would have syntactical meaning

[Rob Cliffe]

On 18/05/2018 12:22, Ken Hilton wrote:
> Hi all,
>
> Yes, this is another idea for avoiding breaking existing code when 
> introducing new keywords. I'm not sure if this is too similar to 
> Guido's previous "allow keywords in certain places" idea, but here goes:
>
> Only treat keywords as having any special meaning when they are in 
> places with syntactical significance.
> So, currently, let's say someone set the variable "and_" to some 
> value. The following lines are both SyntaxErrors:
>
>   True and_ False
>   obj.and = value
>
> And the following are both correct:
>
>   True and False
>   obj.and_ = value
>
> My idea is to only treat keywords as having special meaning when 
> they're in the right place. So the following would all be legal:
>
>   >>> from operator import and
>   >>> var = and(True, False)
>   >>> var
>   False
>   >>> var = True and False
>   >>> var
>   False
>   >>> def except(exc, def):
>   ...     try:
>   ...         return def()
>   ...     except exc as e:
>   ...         return e
>   ...
>   >>> except(ZeroDivisionError, lambda: 1/0)
>   ZeroDivisionError('division by zero',)
>   >>> except(ZeroDivisionError, lambda: 0/1)
>   0.0
>   >>> import asyncio as await #this is already currently legal, but 
> will not be in the __future__
>   >>> async def async(def):
>   ...     return await await.get_event_loop().run_in_executor(None, def)
>   ...
>   >>>
>
> And so on.
>
> What are your thoughts?
>
> ​Sharing,
>
> ​Ken Hilton
> ;
>
Great idea, but why restrict it to keywords?  Why not also allow 
operators to be variable names:
 >>> + = 23
 >>> + + + + +
69
 >>> - = 21
 >>> - -
 >>> -21
There would be some minor ambiguities, e.g. would
     - - - -
evaluate to
     (- -) - (-) # -42
or
     (-) - (- -) # +42
or
     - ( - ( - ( - ))) # -21
or
     - (- - -) # 0
and indeed
     + + + + +
could *in theory* evaluate to
     + ( + ( + ( + ( +)))) # 23
or
     (++) + (++) # 46
but I'm sure we could formulate some sensible rules to always get the 
intended meaning. :-)

Rob Cliffe
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20180519/8d144345/attachment.html>