Extending the import mechanism - what is recommended?

[dbr517 at gmail.com]

On Jan 29, 2:36 pm, Steve Holden <st... at holdenweb.com> wrote:
> dbr... at gmail.com wrote:
> > I need to extend the import mechanism to support another file type.
> > I've already written the necessary C library to read the file and
> > return a python code object.
>
> > I found one example which just sub-classed imputil.ImportManager like
> > this:
>
> > from myLib import pye_code as pye_code
> > class MyImporter(imputil.ImportManager):
> >     def __init__(self):
> >         imputil.ImportManager.__init__(self)
> >         self.add_suffix('.pye', self.import_pye)
> >         self.install()
>
> >     def import_pye(self, filepath, fileinfo, filename):
> >         data = pye_code(filepath)
> >         return 0, data, {}
>
> > This actually works fine if the module is just a few lines of code,
> > but it won't chain to the "built-in" importers; if the module that I'm
> > importing does something as simple as 'import re', it fails.
>
> > It may be that my confusion here is because (even after reading the
> > code), I'm not clear on the purposes of imputil.ImportManager vs.
> > imputil.Importer :-(
>
> > What is the "preferred" way to do this type of extension?  One other
> > note; at this time, I just need to import individual module files with
> > this extension; I don't need to import packages.
>
> Here's an importer I wrote some time ago to bring modules in from a
> relational database. I won't trouble you with the code to compile the
> modules/packages and add them into the database, but perhaps the
> attached code will be enough to show you what you are doing that's not
> working.
>
> regards
>   Steve
> --
> Steve Holden        +1 571 484 6266   +1 800 494 3119
> Holden Web LLC              http://www.holdenweb.com/
>
> [dbimp.py]#
> # Import modules from a database
> #
> # NOTE: could use sys version info to select appropriate module version
> #       - could ask whether to install if absent ... heh, heh :-)
> #
> import sys, db, marshal
> VER = sys.hexversion
----------------------------------->
> def install():
>     sys.path_hooks.append(dbimporter)
>     sys.path_importer_cache.clear() # probably not necessary
>     sys.path.insert(0, "*db*") # probably not needed with a metea-path hook?

Steve -

Thanks!  Got this to work with one interesting problem . . . if I use
sys.path.insert(0....) and insert my hook at the head of the path,
then I can't import anything EXCEPT my special modules . . . If I use
sys.path.append("*pye*") then I'm OK.

One thing I changed was that my load_module function raises
ImportError if it fails; my understanding from reading PEP302 is that
that's what's SUPPOSED to happen . . .

At any rate, I can now import my custom modules . . . thanks!

Dan