[Python-ideas] Move more parts of interpreter core to stdlib

[Antoine Pitrou]

On Mon, 26 Aug 2013 14:54:43 -0400
Ned Batchelder <ned at nedbatchelder.com>
wrote:
> On 8/26/13 1:55 PM, Antoine Pitrou wrote:
> > On Mon, 26 Aug 2013 16:36:53 +0200
> > Draic Kin <drekin at gmail.com> wrote:
> >> Hello, it would be nice if reference pure Python implementation existed for
> >> more parts of interpreter core and the core actually used them. This was
> >> done for import machinery in Python 3.3 making importlib library.
> >>
> >> One potential target for this would be moving the logic of what python.exe
> >> does – parsing its arguments, finding the script to run, compiling its code
> >> and running as __main__ module, running REPL if it's in interactive mode
> >> afterwards. There could be a stdlib module exposing this logic, using
> >> argparse to parse the arguments, overhauled version of runpy to run the
> >> __main__ module and overhauled version of code to run the REPL. Python.exe
> >> would be just thin wrapper which bootstraps the interpreter and runs this
> >> runner module.
> > The interpreter needs a lot of information to be bootstrapped; you are
> > proposing that the code which extracts that information be run *after*
> > the interpreter is bootstrapped, which creates a nasty temporal problem.
> >
> > In the end, it may make maintenance *more* difficult, rather than less,
> > to rewrite that code in Python.
> It seems to me that this argument could have been made against the 
> import rewrite in Python.  I don't know enough about the various factors 
> to know what the differences are between the two scenarios (import and 
> startup) to know whether it's a valid argument here or not. Can someone 
> elaborate?

The import system is algorithmically non-trivial, and it needs to be
easily reusable by outside code. These are two good reasons to write the
implementation in Python. The early startup sequence, on the other
hand, is trivially sequential and can't be reused by user code (by
construction: once the interpreter is initialized, you can't run the
startup sequence again).

The one thing that may be considered is whether there is a point in
having two versions of the interactive prompt: the default one in C,
and a re-usable Python one in code.py.

Regards

Antoine.