[ python-Bugs-1695718 ] PEP 302 broken

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Bugs item #1695718, was opened at 2007-04-06 12:32
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Category: Python Interpreter Core
Group: Python 2.5
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: phil (philipdumont)
Assigned to: Nobody/Anonymous (nobody)
Summary: PEP 302 broken

Initial Comment:
The product I'm working on uses a PEP 302 importer hook.  It's a home-grown ltihooks clone.  (We don't use ltihooks because it's GPLed, and we don't want to be.)

Our importer worked on 2.4.3, is broken on 2.5.0.

What's broken is that if the hook's find_module() method returns None for a given module name, say 'spam', then that is supposed to cause the import machinery to fall back on the regular unhooked import behavior -- that is, find 'spam.py' (or 'spam.pyc', 'spam.pyo') in the directory in question.  This used to be what happened, but no longer.

Tracing through the code, the problem seems to be occurring due to the 'continue' at line 1289 (in the 2.5 tarball) of Python/import.c.

Slogging through SVN (aside: this would have been easier if your ViewSVN supported annotate/blame -- any chance you could add that?), it appears that the offending continue statement was added in revision 46372, whose checkin comment claims that it was done for performance reasons.  I'm all for performance improvements, but not at the expense of breakage.

Attached is a tarball with some files that reproduce the problem.  (The LibtoolImporter.py file is a stripped-down toy version of what we are really using.)  Unwind the tarball, cd to the directory, and run script.py.  Here's what I get:



shell prompt> pwd
/home/phil/pep302_bug
shell prompt> ls -CF
eggs.la  LibtoolImporter.py  script.py*  spam.py
shell prompt> python2.4.3 script.py
.la file(s) found in /home/phil/pep302_bug, LibtoolImporter will be used.
LibtoolImporter.find_module() couldn't find spam.la or spammodule.la
in /home/phil/pep302_bug.  Returning None.  This is *supposed* to cause a
fallback to the default import code looking for spam.py
in /home/phil/pep302_bug
module spam loaded
shell prompt> python2.5 script.py
.la file(s) found in /home/phil/pep302_bug, LibtoolImporter will be used.
LibtoolImporter.find_module() couldn't find spam.la or spammodule.la
in /home/phil/pep302_bug.  Returning None.  This is *supposed* to cause a
fallback to the default import code looking for spam.py
in /home/phil/pep302_bug
Traceback (most recent call last):
  File "script.py", line 4, in <module>
    import spam
ImportError: No module named spam
shell prompt>

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