[Python-Dev] IronPython and AST branch

Brett Cannon brett at python.org
Sat Sep 16 20:33:56 CEST 2006

On 9/13/06, Sanghyeon Seo <sanxiyn at gmail.com> wrote:
> CPython 2.5, which will be released Real Soon Now, is the first
> version to ship with new "AST branch", which have been in development
> for a long time.
> AST branch uses ASDL, Abstract Syntax Description Language
> http://asdl.sourceforge.net/ to describe Abstract Syntax Tree data
> structure used by CPython compiler. In theory this is language
> independant, and the same file could be used to generate C# source
> files.

It would be nice, but see below.

Having the same AST for Python implementations will be good for
> applications and libraries using Python implementations's internal
> parsers and compilers. Currently, those using CPython parser module or
> compiler package can't be easily ported to IronPython.
> What do you think?

I have talked to Jim Hugunin about this very topic at the last PyCon.  He
pointed out that IronPython was started before he knew about the AST branch
so that's why he didn't use it.  Plus, by the time he did know, it was too
late to switch right then and there.

As for making the AST branch itself more of a standard, I have talked to
Jeremy Hylton about that and he didn't like the idea, at least for now.  The
reasons for keeping it as "experimental" in terms of exposure at the Python
level is that we do not want to lock ourselves down to some AST spec that we
end up changing in the future.  It's the same reasoning behind not
officially documenting the marshal format; we want the flexibility.

How best to resolve all of this, I don't know.  I completely understand not
wanting to lock ourselves down to an AST too soon.  Might need to wait a
little while after the AST has been out in the wild to see what the user
response is and then make a decision.

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