[Python-3000] Brainstorming: literal construction hooks

[Michael Urman]

This idea isn't fully fleshed out, but I wanted to air it to see if it
took wind or fell flat. Please forgive inaccuracies between lexing and
parsing.

It's about being able to override what a given literal is turned into.
It would only take effect in a limited scope, either per module, per
compile/exec, or something similar. When a literal of a registered
token type is parsed, its string would be passed to the provided
function and whose return value would be used for the object.  The
following example, when registered, would be used to turn all float
literals into decimal instances.

    def float_literal(literal):
        return decimal.Decimal(literal)

More simply decimal.Decimal could be registered as the literal
constructor if just the literal's string is used. Alternative
signatures could allow a single function to handle multiple token
types, or could make applying modifications to normal types simpler,
but would prevent the obvious use of decimal.Decimal as above. I see
token_type and value (as normally parsed) as obvious candidates for
this.

This could be used for people who want to create auto-substituting
string literals (which I dislike for I18N reasons) without having to
shoehorn its own syntax into the language.

There's a lot of holes to this story, including at least how these
functions are registered, and which additional arguments (if any) are
necessary. Shall we try to fill these holes in?

Michael
--
Michael Urman  http://www.tortall.net/mu/blog