python3.pkgs.scikitlearn: 0.20.3 -> 0.21.2 (#63591)

Splits scikitlearn into a python2 (0.20.x) and a python3 (>0.20)
version.

pkgs/development/python-modules/scikitlearn/0.20.nix

@@ -0,0 +1,38 @@
+{ stdenv, buildPythonPackage, fetchPypi
+, gfortran, glibcLocales
+, numpy, scipy, pytest, pillow
+}:
+
+# 0.20.x is the last version that maintains python2 compatibility
+
+buildPythonPackage rec {
+  pname = "scikit-learn";
+  version = "0.20.3";
+  # UnboundLocalError: local variable 'message' referenced before assignment
+  disabled = stdenv.isi686;  # https://github.com/scikit-learn/scikit-learn/issues/5534
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "c503802a81de18b8b4d40d069f5e363795ee44b1605f38bc104160ca3bfe2c41";
+  };
+
+  buildInputs = [ pillow gfortran glibcLocales ];
+  propagatedBuildInputs = [ numpy scipy numpy.blas ];
+  checkInputs = [ pytest ];
+
+  LC_ALL="en_US.UTF-8";
+
+  doCheck = !stdenv.isAarch64;
+  # Skip test_feature_importance_regression - does web fetch
+  checkPhase = ''
+    cd $TMPDIR
+    HOME=$TMPDIR OMP_NUM_THREADS=1 pytest -k "not test_feature_importance_regression" --pyargs sklearn
+  '';
+
+  meta = with stdenv.lib; {
+    description = "A set of python modules for machine learning and data mining";
+    homepage = http://scikit-learn.org;
+    license = licenses.bsd3;
+    maintainers = with maintainers; [ ];
+  };
+}