[Python-Dev] Fix import errors to have data (original) (raw)

Tim Peters tim.peters at gmail.com
Tue Aug 3 05:14:12 CEST 2004

[Christian Tismer] ...

Yes, but I think you are almost an atom's distance apart off of the final solution. Grab it!

If you mean this:

Maybe it could be as simple as saving a snapshot of sys.modules whenever importing of a module is begun, and if execution of its body doesn't complete, restoring the snapshot?

then no, that's a long way off in CPython. There's no choke point for when importing begins, or for when importing ends, and even builtin.import is routinely replaced. Guido latched on to the only choke point there is: sooner or later, every import gimmick worthy of the name has to execute "the module's" code, whether it be direct import from Python, directly via C API calls, implicit package init.py imports, imports arranged via magical importers (like the .zip importer), etc. So that's what the patch targeted: there's one routine that executes a module's initialization code, all imports go thru it eventually, and that's the routine that now removes the module's name from sys.modules if the initialization code barfs.

"The rest" of import logic is sprayed all over creation. To hook "begin import" and "end import" first requires that all importers be changed to have a formal notion of those events. The easiest start would be to use bytecodehacks to inject "call begin_import" and "call end_import" opcode sequences around the code generated for import statements <0.8 wink>.

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