Up to Python3.2, a nested ImportError was correctly displayed:

./python -c "import distutils.msvc9compiler"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/amauryfa/python/cpython3.2/Lib/distutils/msvc9compiler.py", line 27, in <module>
    import winreg
ImportError: No module named winreg

But with 3.3, the traceback is lost:

~/python/cpython3.x$ ./python -c "from distutils import msvc9compiler"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: cannot import name msvc9compiler

Even though the failure is still on the "import winreg" line. Only ImportError seems affected, other exceptions are correctly displayed.

To clarify Amaury's example:

rdmurray@hey:~/python/p32>./python -c "from distutils import msvc9compiler"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/rdmurray/python/p32/Lib/distutils/msvc9compiler.py", line 27, in <module>
    import winreg
ImportError: No module named winreg

rdmurray@hey:~/python/p33>./python -c "from distutils import msvc9compiler"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: cannot import name msvc9compiler

So there is definitely some lost information in 3.3 compared to 3.2 in the 'import from' case.

That "cannot import name" message seems to only come from Python/ceval.c:import_from() which raises that exception when an AttributeError is raised by an 'import from' statement (I think). This happens when an 'import from' asks for a name on the package/module that doesn't exist.

Looking at importlib, I found the code that captures the ImportErrorof a submodule, which allows the import to continue and then fail as an AttributeError at the bytecode level. I'm running the test suite now with that try/except removed to see if this was just a mis-interpretation on my part of how to handle this situation. As of right now the only failures I have continue my belief that import * is evil.

New changeset dc18a2a66d16 by Brett Cannon in branch 'default':
Issue #15111: When a module was imported using a 'from import'
http://hg.python.org/cpython/rev/dc18a2a66d16

I don't know why, but it seems that the bug reappeared in 3.3.

Examples:

1. --------------- (python 3.4 from repo)

yury@sxair ~/dev/py/python (master) $ ./python.exe 
Python 3.4.0a0 (default, Oct  5 2012, 15:08:35) 
[GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.65))] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from distutils import msvc9compiler
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cannot import name msvc9compiler

2. --------------- (python 3.3.0 from macports)

yury@sxair ~/dev/py/python (master) $ python3.3
Python 3.3.0 (default, Oct  5 2012, 13:41:24) 
[GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.65))] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from distutils import msvc9compiler
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cannot import name msvc9compiler


3. ----------- (python 3.2 from macports)

yury@sxair ~/dev/py/python (master) $ python3.2
Python 3.2.2 (default, Sep 27 2012, 13:31:01) 
[GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.65))] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from distutils import msvc9compiler
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/distutils/msvc9compiler.py", line 27, in <module>
    import winreg
ImportError: No module named winreg

Platform: macos x 10.8

Please reopen the issue.

> I don't know why, but it seems that the bug reappeared in 3.3.

Part of it could be that the original fix added no tests.

http://hg.python.org/cpython/rev/dc18a2a66d16 did add a test, just not the right one.

Actually, I take it back, it removed a test without adding a new one. Obviously that's my bad.

Brett, can we patch 3.3 too? (in 3.3.1 version?)

This can get fixed in 3.3.1, which is why I left Python 3.3 as an affected version.

Hopefully I can get to a fix this week. I need to write a test showing that a module that doesn't exist as specified in a fromlist is silently ignored, but if a module in a fromlist does exist *but* triggers an ImportError itself while being imported that exception propagates. Then I need to come up with a fix.

Here are two possible tests.

1) __import__('distutils', fromlist=['_i_do_not_exist']) should return distutils

2) Use a fake loader which executes some code which does nothing more than tries to import a non-existent module. The trick with this test is that the submodule must be found but a module that the submodule needs cannot be found by import itself (and simply not faked with an ImportError thanks to the _not_found hack and needing that attribute to propagate up to the submodule search).

And I think the failure stems from the lack of check against exc.name equaling the name of the module being imported (e.g. exc.name == distutils.msvc9compiler) since the winreg import is a failed module search as well.

New changeset 09b5158d5284 by Brett Cannon in branch '3.3':
Closes issue #15111: Calling __import__ with a module specified in
http://hg.python.org/cpython/rev/09b5158d5284

New changeset 31db8e3272f1 by Brett Cannon in branch 'default':
Merge fix for issue #15111.
http://hg.python.org/cpython/rev/31db8e3272f1