[Python-ideas] Retain string form of AST Numbers

[Serhiy Storchaka]

05.04.14 06:50, Chris Angelico написав(ла):
> Currently, parsing a Python script into an AST discards a huge amount
> of information. Some of that (line and column information) is retained
> as metadata, but a lot isn't. One of the potentially-useful things
> that's currently dropped is the string form of numbers:
>
>>>> print(ast.dump(ast.parse("x = 1 + 2.000 + 3.0j")))
> Module(body=[Assign(targets=[Name(id='x', ctx=Store())],
> value=BinOp(left=BinOp(left=Num(n=1), op=Add(), right=Num(n=2.0)),
> op=Add(), right=Num(n=3j)))])
>
> The three Num nodes have an n with the already-constructed
> int/float/complex. At this point, it's impossible to return to the
> original string that was entered; any rounding will have already taken
> place.
>
> If the Num nodes also had a .str member with the unparsed string ("1",
> "2.000", and "3.0j"), it would be possible to influence their
> interpretation with an AST transform - for instance, turning them into
> decimal.Decimal construction calls, or wrapping them in something that
> automatically keeps track of significant figures (which would mean
> that "2.000" is considered more precise than a mere "2.0" or "2.").
>
> It shouldn't be too difficult to do, and it could simply be ignored in
> most cases; any sort of change to the actual number could leave the
> original string out of sync with it, which isn't a problem.
>
> Thoughts?

What about strings?

 >>> print(ast.dump(ast.parse(r"x = '''\x0a\u000d''' r'x'")))
Module(body=[Assign(targets=[Name(id='x', ctx=Store())], 
value=Str(s='\n\rx'))])

Tuples?

 >>> print(ast.dump(ast.parse("x = (1, 2,)")))
Module(body=[Assign(targets=[Name(id='x', ctx=Store())], 
value=Tuple(elts=[Num(n=1), Num(n=2)], ctx=Load()))])