try to fix pickling

nifty5/operators/harmonic_operators.py

@@ -289,6 +289,11 @@ class SHTOperator(LinearOperator):
         else:
             self.sjob.set_Healpix_geometry(target.nside)
 
+    def __reduce__(self):
+        print ("reduce")
+        return (_unpickleSHTOperator,
+                (list(self._domain), self._target[self._space], self._space))
+
     def apply(self, x, mode):
         self._check_input(x, mode)
         if utilities.iscomplextype(x.dtype):
@@ -337,6 +342,11 @@ class SHTOperator(LinearOperator):
         return Field(tdom, dobj.ensure_default_distributed(odat))
 
 
+def _unpickleSHTOperator(*args):
+    print ("unpickle")
+    return SHTOperator(*args)
+
+
 class HarmonicTransformOperator(LinearOperator):
     """Transforms between a harmonic domain and a position domain counterpart.