buildPythonPackage: refactor

pkgs/development/interpreters/python/build-python-package-common.nix

@@ -0,0 +1,27 @@
+# This function provides generic bits to install a Python wheel.
+
+{ python
+, bootstrapped-pip
+}:
+
+{ buildInputs ? []
+# Additional flags to pass to "pip install".
+, installFlags ? []
+, ... } @ attrs:
+
+attrs // {
+  buildInputs = buildInputs ++ [ bootstrapped-pip ];
+
+  installPhase = attrs.installPhase or ''
+    runHook preInstall
+
+    mkdir -p "$out/${python.sitePackages}"
+    export PYTHONPATH="$out/${python.sitePackages}:$PYTHONPATH"
+
+    pushd dist
+    ${bootstrapped-pip}/bin/pip install *.whl --no-index --prefix=$out --no-cache ${toString installFlags}
+    popd
+
+    runHook postInstall
+  '';
+}