Instead of removing just the import, we should copy-paste the full file in case that some bug fixes have been applied there.

@glemaitre I'm agree to copy if possible, but from where? Again, while these files originate in SciPy, they have been removed from SciPy and are now maintained here.

See initial PR #10427.

See also previous history of these files, they have already been modified multiple times:
https://github.com/scikit-learn/scikit-learn/commits/main/sklearn/externals/_lobpcg.py
https://github.com/scikit-learn/scikit-learn/commits/main/sklearn/externals/_pilutil.py

While scipy/misc/pilutil.py had been removed in scipy/scipy#9325, I can still find a scipy/sparse/linalg/eigen/lobpcg/lobpcg.py file. Let me double-check that file.

I'll move _pilutil.py to sklearn/utils in a different PR.

Actually scipy/sparse/linalg/eigen/lobpcg/lobpcg.py starts with:

"""
scikit-learn copy of scipy/sparse/linalg/eigen/lobpcg/lobpcg.py v1.3.0
to be deleted after scipy 1.3.0 becomes a dependency in scikit-lean
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

This file was supposed to removed for SciPy 1.3.0, but it's actually still there! I might open an issue in SciPy about it. I'll copy the latest version here in an upcoming PR.

I have created #21163 to update _lobpcg.py since it's still there. I'll rework this PR.

I might open an issue in SciPy about it. I'll copy the latest version here in an upcoming PR.

No need to be open an issue. The comment is still meaningful. Our minimum requirement is SciPy 1.1.0 that is lower than 1.3.0 when lobpcg was introduced in SciPy. We still need to wait until we bump the version. However, we should copy the current SciPy version into our externals file.

I think that we should tag this PR for 1.0.1 to have the latest lobpcg in our release indeed. I don't know if it includes some bug fixes thought.

Ah, got it! I thought that file was supposed to be deleted in SciPy 1.3.0, not introduced in SciPy 1.3.0.

"""
scikit-learn copy of scipy/sparse/linalg/eigen/lobpcg/lobpcg.py v1.3.0
to be deleted after scipy 1.3.0 becomes a dependency in scikit-lean
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

I think that we should tag this PR for 1.0.1 to have the latest lobpcg in our release indeed. I don't know if it includes some bug fixes thought.

Yes, I think there were some bugs (see maxIteration vs. maxiter).

I have changed this PR to update _pilutil.py only.

The other file, _lobpcg.py, is updated in #21163.

I think that we should tag this PR for 1.0.1 to have the latest lobpcg in our release indeed. I don't know if it includes some bug fixes thought.

I don't like doing this kind of change in a bugfix release. I think it's fine to do the cleanup later.

Edit: if there are some bugs, then ok to consider it a bug fix but it should be documented as such in the 1.0.1 changelog.

Looking at the diff, it does not seem like a bug fix, only a renaming of maxIteration to maxiter and a fix in the docstring of the function (which is not part of the scikit-learn public API).

Looking at the diff, it does not seem like a bug fix, only a renaming of maxIteration to maxiter and a fix in the docstring of the function (which is not part of the scikit-learn public API).

So we can post-pone for 1.1 release. We will not need any changelog even.

+1 for merging #21163 as is. And I am still +1 for merging this PR as is.

Thanks @DimitriPapadopoulos