pythonPackages.caldav: unbreak build

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

@@ -1,5 +1,12 @@
-{ lib, buildPythonPackage, fetchPypi
-, tzlocal, requests, vobject, lxml, nose }:
+{ lib
+, buildPythonPackage
+, fetchPypi
+, tzlocal
+, requests
+, vobject
+, lxml
+, nose
+}:
 
 buildPythonPackage rec {
   pname = "caldav";
@@ -12,11 +19,16 @@ buildPythonPackage rec {
     sha256 = "80c33b143539da3a471148ac89512f67d9df3a5286fae5a023e2ad3923246c0d";
   };
 
+  # xandikos is only a optional test dependency, not available for python3
+  postPatch = ''
+    substituteInPlace setup.py \
+      --replace ", 'xandikos'" ""
+  '';
+
   meta = with lib; {
     description = "This project is a CalDAV (RFC4791) client library for Python.";
     homepage = "https://pythonhosted.org/caldav/";
     license = licenses.asl20;
     maintainers = with maintainers; [ marenz ];
-    broken = true; # missing xandikos package
   };
 }