Added support for _H-M_ref space group keyword

Author: rozyczko

Diff for: src/diffpy/structure/parsers/p_cif.py

@@ -472,6 +472,7 @@ def _parse_space_group_symop_operation_xyz(self, block):
         sg_nameHall = (block.get('_space_group_name_Hall', '') or
                 block.get('_symmetry_space_group_name_Hall', ''))
         sg_nameHM = (block.get('_space_group_name_H-M_alt', '') or
+                block.get('_space_group_name_H-M_ref', '') or
                 block.get('_symmetry_space_group_name_H-M', ''))
         self.cif_sgname = (sg_nameHall or sg_nameHM or None)
         sgid = (block.get('_space_group_IT_number', '') or

Diff for: src/diffpy/structure/tests/testp_cif.py

@@ -71,6 +71,7 @@ class TestP_cif(unittest.TestCase):
     graphiteciffile = datafile('graphite.cif')
     cdsebulkpdffitfile = datafile('CdSe_bulk.stru')
     teiciffile = datafile('TeI.cif')
+    refciffile = datafile('Ni_ref.cif')
     places = 6
 
 
@@ -334,6 +335,14 @@ def test_spacegroup_anisotropy(self):
         self.assertTrue(all(stru.anisotropy))
         return
 
+    def test_spacegroup_ref(self):
+        "verify space group reference"
+        pfile = self.pfile
+        pfile.parseFile(self.refciffile)
+        sg = pfile.spacegroup
+        self.assertEqual('Fm-3m', sg.short_name)
+
+        return
 
     def test_adp_type_ani(self):
         "verify adp type override to anisotropic"