[Python-Dev] is this the fault of import_fresh_module or pickle? (original) (raw)

Eli Bendersky eliben at gmail.com
Tue Jan 8 17:58:46 CET 2013

On Tue, Jan 8, 2013 at 8:37 AM, R. David Murray <rdmurray at bitdance.com>wrote:

On Tue, 08 Jan 2013 17:05:50 +0100, Stefan Krah <stefan at bytereef.org> wrote: > Eli Bendersky <eliben at gmail.com> wrote: > > Everything works fine. However, if I add importfreshmodule for the C module: > > > > from test.support import importfreshmodule > > import pickle > > C = importfreshmodule('xml.etree.ElementTree', fresh=['elementtree']) > > P = importfreshmodule('xml.etree.ElementTree', blocked=['elementtree']) > > sys.modules still contains the C version at this point, so: > > sys.modules['xml.etree.ElementTree'] = P > > > > tb = P.TreeBuilder() > > print(pickle.dumps(tb)) > > > This interaction only seems to happen with pickle. What's going on here? Can we > > somehow improve importfreshmodule to avoid this? Perhaps actually deleting > > previously imported modules with some special keyword flag? > > pickle always looks up sys.modules['xml.etree.ElementTree']. Perhaps we > could improve something, but this requirement is rather special; personally > I'm okay with switching sys.modules explicitly in the tests, because that > reminds me of what pickle does.

Handling this case is why having a context-manager form of importfreshmodule was suggested earlier in this meta-thread. At least, I think that would solve it, I haven't tried it :)

Would you mind extracting just this idea into this discussion so we can focus on it here? I personally don't see how making import_fresh_module a context manager will solve things, unless you add some extra functionality to it? AFAIU it doesn't remove modules from sys.modules before importing, at this point.

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