New submission from Larry Hastings <la...@hastings.org>:
While working on another issue, I noticed two minor nits in the C
implementation of the module object. Both are related to getting a module's
name.
--
First, the C function module_dir() (module.__dir__) starts by ensuring the
module dict is valid. If the module dict is invalid, it wants to format an
exception using the name of the module, which it gets from PyModule_GetName().
However, PyModule_GetName() gets the name of the module from the dict. So
getting the name in this circumstance will never succeed.
When module_dir() wants to format the error but can't get the name, it knows
that PyModule_GetName() must have already raised an exception. So it leaves
that exception alone and returns an error. The end result is that the
exception raised here is kind of useless and misleading: dir(module) on a
module with no __dict__ raises SystemError("nameless module"). I changed the
code to actually raise the exception it wanted to raise, just without a real
module name: TypeError("<module>.__dict__ is not a dictionary"). This seems
more useful, and would do a better job putting the programmer who encountered
this on the right track of figuring out what was going on.
--
Second, the C API function PyModule_GetNameObject() checks to see if the module
has a dict. If m->md_dict is not NULL, it calls _PyDict_GetItemIdWithError().
However, it's possible for m->md_dict to be None. And if you call
_PyDict_GetItemIdWithError(Py_None, ...) it will *crash*.
Unfortunately, this crash was due to my own bug in the other branch. Fixing my
code made the crash go away. I assert that this is still possible at the API
level.
The fix is easy: add a PyDict_Check() to PyModule_GetNameObject().
Unfortunately, I don't know how to add a unit test for this. Having changed
module_dir() above, I can't find any other interfaces callable from Python that
eventually call PyModule_GetNameObject(). So I don't know how to trick the
runtime into reproducing this error.
----------
assignee: larry
components: Interpreter Core
messages: 392055
nosy: larry
priority: normal
severity: normal
stage: needs patch
status: open
title: Two minor fixes for C module object
type: behavior
versions: Python 3.10
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue43951>
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