[Python-ideas] Default arguments in Python - the return - running out of ideas but...

[George Sakkis]

On Wed, May 13, 2009 at 10:52 AM, Jeremy Banks <jeremy at jeremybanks.ca> wrote:

> To someone who's a novice to this, could someone explain to me why it
> has to be an existing keyword at all? Since not identifiers are valid
> in that context anyway, why couldn't it be a new keyword that can
> still be used as an identifier in valid contexts? For example (not
> that I advocate this choice of keyword at all):
>
>    def foo(bar reinitialize_default []): # <-- it's a keyword here
>        reinitialize_default = "It's an identifier here!"
>
> That would be a syntax error now and if it were defined as a keyword
> only in that context it wouldn't introduce backwards compatibility
> problems and wouldn't force us to reuse an existing keyword in a
> context that may be a bit of a stretch.
>
> Is there a reason that this wouldn't be a viable approach?

Traditionally, keywords are recognized at the lexer level, which then
passes tokens to the parser. Lexers are pretty simple (typically
constants and regular expressions) and don't take the context into
account. In principle what you're saying could work, but given the
significant reworking of the lexer/parser it would require, it's quite
unlikely to happen, for better or for worse.

George