[Python-Dev] importlib is now bootstrapped (and what that means)

Brett Cannon brett at python.org
Mon Apr 16 19:32:59 CEST 2012

On Mon, Apr 16, 2012 at 13:04, "Martin v. Löwis" <martin at v.loewis.de> wrote:

> > I don't see how depending on Cython is better than depending on having
> > an existing Python.  If the only benefit is semi-readable code, surely
> > we do have source code for the pre-frozen module, and it is just a matter
> > of convincing hg that the bytecode is binary, not text?
> Cython-generated C code would likely be more stable (and produce
> compiler errors if it gets stale), whereas importlib.h needs to be
> regenerated with byte code changes.
> Having source code has the advantage that it becomes possible to
> single-step through the import process in C debugger. Single-stepping
> with pdb would, of course, be better than that, but I doubt it's
> feasible.
> In addition, there might be a performance gain with Cython over ceval.

The other benefit is maintainability. In order to hit my roughly 5% startup
speed I had to rewrite chunks of __import__() in C code and then delegate
to importlib's Python code in cases where sys.modules was not hit. Using
Cython would mean that can all go away and the differences between the C
and Python code would become (supposedly) non-existent, making tweaks
easier (e.g. when I made the change to hit sys.modules less when a loader
returned the desired module it was annoying to have to change importlib
*and* import.c).
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