"as" keyword woes
tjreedy at udel.edu
Sat Dec 6 22:47:15 CET 2008
Warren DeLano wrote:
> As someone somewhat knowledgable of how parsers work, I do not
> understand why a method/attribute name "object_name.as(...)" must
> necessarily conflict with a standalone keyword " as ". It seems to me
> that it should be possible to unambiguously separate the two without
> ambiguity or undue complication of the parser.
The lexer, which preceeds the parser, has separate KEYWORD and
IDENTIFIER categories. For example, 'if a ...' is lexed as (KEYWORD,
'if'), (IDENTIFIER, 'a'), ... . Leaving 'as' as an identifier
identified by the parser as a contextual keyword in import statements
was a kludge. When 'as' was reused in "with <expr> as <target>" in 2.5
(with __future__ import), it was planned and announced that *both*
'with' and 'as' would become full-time keywords in 2.6, just as 'yield'
did in 2.3 after its introduction (with required __future__) in 2.2.
Making 'yield' a keyword of course impacted people who used the word in
financial calculations, but they adjusted.
> So, assuming I now wish to propose a corrective PEP
Working with people trying to improve threading would be more productive.
Terry Jan Reedy
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