Some Cython implementations use interfaces from the standard library of C++, namely std::algorithm::move and std::algorithm::fill from std::algorithm.

Before Cython 3, those interfaces had to be imported directly using the verbose syntax from Cython:

• scikit-learn/sklearn/metrics/_pairwise_distances_reduction/_radius_neighbors.pyx.tp

  Lines 22 to 26 in 5fc67ae

  	# TODO: change for `libcpp.algorithm.move` once Cython 3 is used
  	# Introduction in Cython:
  	# https://github.com/cython/cython/blob/05059e2a9b89bf6738a7750b905057e5b1e3fe2e/Cython/Includes/libcpp/algorithm.pxd#L47 #noqa
  	cdef extern from "<algorithm>" namespace "std" nogil:
  	OutputIt move[InputIt, OutputIt](InputIt first, InputIt last, OutputIt d_first) except + #noqa

• scikit-learn/sklearn/metrics/_pairwise_distances_reduction/_middle_term_computer.pyx.tp

  Lines 28 to 33 in 5fc67ae

  	# TODO: change for `libcpp.algorithm.fill` once Cython 3 is used
  	# Introduction in Cython:
  	#
  	# https://github.com/cython/cython/blob/05059e2a9b89bf6738a7750b905057e5b1e3fe2e/Cython/Includes/libcpp/algorithm.pxd#L50 #noqa
  	cdef extern from "<algorithm>" namespace "std" nogil:
  	void fill[Iter, T](Iter first, Iter last, const T& value) except + #noqa

Cython 3 introduced the following line natively, for those interfaces. Those interfaces should now be cimported directly. That is one can replace the line shown above respectively with:

from libcpp.algorithm cimport move
from libcpp.algorithm cimport fill

I believe this is a good first Cython issue.

Any reader should feel free to pick it up. It might be possible that there is some context missing.

Please let me know if you need help. 🙂