pythonPackages.libcst: init at 0.3.12

I am adding this package because it is a dependency of
google_cloud_dataproc.

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

@@ -0,0 +1,36 @@
+{ stdenv
+, buildPythonPackage
+, fetchPypi
+, typing-inspect
+, pyyaml
+, isPy3k
+}:
+
+buildPythonPackage rec {
+  pname = "libcst";
+  version = "0.3.12";
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "1zgwxdbhz2ljl0yzbrn1f4f464rjphx0j6r4qq0csax3m4wp50x1";
+  };
+
+  # The library uses type annotation syntax.
+  disabled = !isPy3k;
+
+  propagatedBuildInputs = [ typing-inspect pyyaml ];
+
+  # Test fails with ValueError: No data_provider tests were created for
+  # test_type_availability! Please double check your data.
+  # The tests appear to be doing some dynamic introspection, not sure what is
+  # going on there.
+  doCheck = false;
+  pythonImportsCheck = [ "libcst" ];
+
+  meta = with stdenv.lib; {
+    description = "A concrete syntax tree parser and serializer library for Python that preserves many aspects of Python's abstract syntax tree";
+    homepage = "https://libcst.readthedocs.io/en/latest/";
+    license = with licenses; [mit asl20 psfl];
+    maintainers = [ maintainers.ruuda ];
+  };
+}

pkgs/top-level/python-packages.nix

@@ -3275,6 +3275,8 @@ in {
   else
     callPackage ../development/python-modules/libcloud { };
 
+  libcst = callPackage ../development/python-modules/libcst { };
+
   libevdev = callPackage ../development/python-modules/libevdev { };
 
   libfdt = toPythonModule (pkgs.dtc.override {