[Python-3000] Brainstorming: literal construction hooks

[Nick Coghlan]

Guido van Rossum wrote:
> On 4/22/06, Nick Coghlan <ncoghlan at gmail.com> wrote:
>> Michael Urman wrote:
>>> 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?
>> Answering without checking the source (which is undoubtedly a bad idea), but
>> this sounds like something else that could be addressed if it was possible to
>> either register an alternate AST compiler for a scope, or else get hold of an
>> AST and recompile it. (The former works for modules and functions, the latter
>> works only for functions)
>>
>> Even if it was only a matter of some additional keyword arguments to compile
>> and/or exec, it could at least be of benefit for plugin code or an interactive
>> interpreter loop.
> 
> Hm... Using the AST seems overkill for this (unless you want to do it
> without modifying the Python interpreter in any way).

Strawman. . .

from ast import Compiler
from decimal import Decimal

class MyCompiler(Compiler):
   def build_float(self, literal):
       return Decimal(literal)

# Pass this to compile or exec via an ast_compiler argument
# It may even be possible to permit it as an argument to __import__

The basic idea would be to have a compiler object that delegated compilation 
operations to the internal AST compiler, but gave subclasses the ability to 
easily override certain aspects of the process - like processing different 
kinds of literal.

No matter what, permitting these kinds of hooks is going to require 
alterations to the process of compiling the AST to the bytecode - and 
subclassing is an excellent way of allowing some aspects of an implementation 
to be overridden while leaving other aspects alone.

This is just an idea, as I doubt I'd ever use the ability no matter how it was 
implemented :)

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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