python.pkgs.pystemmer: fix compilation with python3.7

pkgs/development/python-modules/pystemmer/default.nix

@@ -0,0 +1,28 @@
+{ stdenv, python, fetchPypi, buildPythonPackage, cython }:
+
+buildPythonPackage rec {
+  pname = "PyStemmer";
+  version = "1.3.0";
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "d1ac14eb64978c1697fcfba76e3ac7ebe24357c9428e775390f634648947cb91";
+  };
+
+  nativeBuildInputs = [ cython ];
+
+  preBuild = ''
+    cython src/Stemmer.pyx
+  '';
+
+  checkPhase = ''
+    ${python.interpreter} runtests.py
+  '';
+
+  meta = with stdenv.lib; {
+    description = "Snowball stemming algorithms, for information retrieval";
+    homepage = http://snowball.tartarus.org/;
+    license = licenses.mit;
+    platforms = platforms.unix;
+  };
+}

pkgs/top-level/python-packages.nix

@@ -10966,25 +10966,7 @@ in {
     };
   };
 
-  PyStemmer = buildPythonPackage (rec {
+  PyStemmer = callPackage ../development/python-modules/pystemmer {};
-    name = "PyStemmer-1.3.0";
-
-    src = pkgs.fetchurl {
-      url = "mirror://pypi/P/PyStemmer/${name}.tar.gz";
-      sha256 = "d1ac14eb64978c1697fcfba76e3ac7ebe24357c9428e775390f634648947cb91";
-    };
-
-    checkPhase = ''
-      ${python.interpreter} runtests.py
-    '';
-
-    meta = {
-      description = "Snowball stemming algorithms, for information retrieval";
-      homepage = http://snowball.tartarus.org/;
-      license = licenses.mit;
-      platforms = platforms.unix;
-    };
-  });
 
   Pyro = callPackage ../development/python-modules/pyro { };