gh-69605: Check for already imported modules in PyREPL module completion

[loic-simon]

This PR handles an edge-case when suggesting module imports in PyREPL (see this comment):

If a module is already imported, the import machinery will only get submodules from it, even if a module of the same name is higher in the path. This can happen if eg. sys.path has been updated since the module was originaly imported.

The easiest way to reproduce this issue (and how I stumbled on it) is with stdlib modules imported during interpreter startup (before site customisation, so ignoring potential shadowing):

% mkdir collections
% touch collections/__init__.py collections/foo.py
% python
Python 3.14.0rc2 [...]
>>> from collections import <TAB>
>>> from collections import foo
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    from collections import foo
ImportError: cannot import name 'foo' from 'collections' (/Users/loic/cpython/Lib/collections/__init__.py)
>>>

---

This PR add a special case in _pyrepl.ModuleCompleter._find_modules that

• check if the module to complete imports from is already imported
• if yes, search for imports from the imported module location only, instead of using the global cache

It was a little tricky to get right, I'm not sure about everything 😅 but it pass all tests I could think off!

cc @tomasr8

• Issue: Readline completion of module names in import statements #69605

[loic-simon]

Ok, one of the new test fails on Windows x64/32 (but pass on arm)

I just setup and built Python on a Win 11 x64 to try to reproduce, the test pass 😵‍💫 (and the fix works)
If anyone has an idea of what may interfere? (Python 3.15.0a0 (main, Sep 30 2025, 23:36:53) [MSC v.1944 64 bit (AMD64)] on win32)

[python-cla-bot]

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[picnixz]

I'm going to convert it into a draft until you deem this PR ready. That will also reduce the probability of someone clicking on the PR to review it (like me...) while it's not yet ready for.

[loic-simon]

I'm going to convert it into a draft until you deem this PR ready. That will also reduce the probability of someone clicking on the PR to review it (like me...) while it's not yet ready for.

Thanks, I just fixed the failing test, this should be ready for review!

Sorry again for the noise, I was dealing with what turned out to be a importer cache issue, which I couldn't reproduce outside of the CI buildbots 😓

[edit] I just noticed I can convert to draft / mark ready myself, will do it next times!