[Python-Dev] clarifying PEP 302 loader responsibilities upon failure (original) (raw)

Brett Cannon bcannon at gmail.com
Sun Feb 15 07:07:07 CET 2009

On Mon, Feb 9, 2009 at 14:02, Guido van Rossum <guido at python.org> wrote:

On Mon, Feb 9, 2009 at 1:56 PM, <bcannon at gmail.com> wrote: > Guido and I were discussing what a loader should be responsible for when > loadmodule is called and an exception is raised in relation to sys.modules > as PEP 302 says nothing about the topic. > > We both agree that if the loader added a module to sys.modules it should be > removed, otherwise it should be left alone. > > Assuming no one disagrees I will update the PEP to specify that this is the > expected job of loaders.

(Note that currently most loaders we've looked at end up removing the module unconditionally, as this is what PyImportExecCodeModuleEx() does. PyImportReloadModule() has a super-duper hack to save the module object and put it back into sys.modules: if (newm == NULL) { /* loadmodule probably removed name from modules because of * the error. Put back the original module object. We're * going to return NULL in this case regardless of whether * replacing name succeeds, so the return value is ignored. */ PyDictSetItemString(modules, name, m); } If we could get conforming loaders to behave as proposed, we wouldn't need this ugly hack.

PEP 302 was updated in r69632.

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