[Python-ideas] A nice __repr__ for the ast.* classes?

[Haoyi Li]

Isn't that the distinction between repr() and str()? That repr() is
generally (to a greater extent) meant to return eval()-able code, while
str() is just something nice to look at.

I don't think the # of pages it outputs should really matter, if the thing
you are printing really is that big. It won't be much bigger than printing
big lists or dicts, and we happily let those cause the terminal to scroll
for minutes at a time if we accidentally print them. The default behavior
(e.g. when you print() it or string-interpolate it) would still give you
something short and nice to look at. Presumably when someone called repr()
instead of str(), he was hoping for some sort of eval()-able code snippet.


On Tue, Apr 30, 2013 at 6:21 PM, Guido van Rossum <guido at python.org> wrote:

> But do you really want it to print the entire parse tree even if it
> represents several pages of code?
>
> On Tue, Apr 30, 2013 at 6:12 PM, Haoyi Li <haoyi.sg at gmail.com> wrote:
> > Wouldn't it be nice if this
> >
> >>>> import ast
> >>>> print repr(ast.parse("(1 + 1)").body[0].value)
> > <_ast.BinOp object at 0x0000000001E94B38>
> >
> > printed something more useful?
> >
> >>>> print repr(ast.parse("(1 + 1)").body[0].value)
> > BinOp(left=Num(n=1), op=Add(), right=Num(n=1))
> >
> > I've been doing some work on macropy, which uses the ast.* classes
> > extensively, and it's annoying that we have to resort to dirty-tricks
> like
> > monkey-patching the AST classes (for CPython 2.7) or even monkey-patching
> > __builtin__.repr (to get it working on PyPy) just to get
> >
> >     eval(repr(my_ast)) == my_ast
> >
> > to hold true. And a perfectly good solution already exists in the
> ast.dump()
> > method, too! (It would also be nice if "==" did a structural comparison
> on
> > the ast.* classes too, but that's a different issue).
> >
> > -Haoyi
> >
> > _______________________________________________
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> > Python-ideas at python.org
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> >
>
>
>
> --
> --Guido van Rossum (python.org/~guido)
>
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