[Python-Dev] Clarifications for import PEPs (302 and 328)

[Brett Cannon]

On 4/23/07, Phillip J. Eby <pje at telecommunity.com> wrote:
> At 04:23 PM 4/23/2007 -0700, Brett Cannon wrote:
> >On 4/23/07, Phillip J. Eby <pje at telecommunity.com> wrote:
> > > At 03:16 PM 4/23/2007 -0700, Brett Cannon wrote:
> > > >The PEP does not explicitly state how to signal that a loader cannot
> > > >load a module it is asked to.  This could happen if someone called a
> > > >loader without consulting its respective importer.  I would want to
> > > >add something like:
> > > >"""
> > > >If the loader is unable to load the specified module and a specific
> > > >exception is not raised in determining this, ImportError is raised.
> > > >This may occur if a loader is called without first consulting an
> > > >importer as to if the loader can load the specified module but the
> > > >loader is aware of the fact it cannot fulfill the request made.
> > > >"""
> > >
> > > Okay, now I understand what you're trying to say, but I still don't
> > > understand what the purpose is.  I mean, what else would you do except
> > > raise an error?  I.e., isn't the actual contract "load the specified module
> > > or raise an exception of some kind"?
> >
> >Not if you read the PEP.  It doesn't explicitly say what should happen.
> >
> >I want to standardize on raising ImportError.  The PEP itself has two
> >ways of signaling an error; find_module() returns None instead of
> >raising an error to signal it can't do something while path hooks
> >raise ImportError.  I just want to be as explicit as possible.
>
> Ok, so this should at least lose the passive voice ("ImportError is
> raised") -- it should say that it's the loader's job to raise
> ImportError.  Otherwise, it's not actually removing any ambiguity.
>

Yeah, the paragraph was from the cuff.

> I also don't find the "This may occur" sentence to be helpful; it seems we
> should just say, "load_module() must return a loaded module or raise an
> error, preferably an ImportError unless an existing exception is being
> propagated."
>
> Meanwhile, if you also mean to say that load_module() is explicitly allowed
> to fail with an ImportError when it's asked for any module other than the
> one it was obtained for (via find_module()), then let's say that, too.
>

Yes, I do mean that.

> Notice, by the way, that this is a stronger condition than the one you
> proposed, yet it doesn't imply that there is or should be an ongoing
> relationship between the loader and the importer.  It also doesn't imply
> that perhaps it's okay for a loader to not succeed in reloading the *same*
> module!  (i.e., as I understand it, a module can currently invoke
> __loader__.load_module(__name__) as a rough synonym for reload().)

Makes sense.

I will make the changes when I have a working laptop again.  Thanks
for the input, Phillip!

-Brett