Add a space group string representation, tested

.gitignore

@@ -42,3 +42,9 @@ nosetests.xml
 # version information
 setup.cfg
 /src/diffpy/*/version.cfg
+
+# PyCharm
+.idea
+
+# Coverage report
+htmlcov

src/diffpy/structure/spacegroupmod.py

@@ -262,6 +262,19 @@ def __init__(self,
         self.pdb_name                = pdb_name
         self.symop_list              = symop_list
 
+    def __repr__(self):
+        """Return a string representation of the space group."""
+        return (
+                   "SpaceGroup #%i (%s, %s). Symmetry matrices: %i, "
+                   "point sym. matr.: %i"
+               ) % (
+            self.number,
+            self.short_name,
+            self.crystal_system[0] + self.crystal_system[1:].lower(),
+            self.num_sym_equiv,
+            self.num_primitive_sym_equiv,
+        )
+
 
     def iter_symops(self):
         """Iterate over all symmetry operations in the space group.

src/diffpy/structure/tests/testspacegroups.py

@@ -86,6 +86,35 @@ def test__hashSymOpList(self):
         self.assertEqual(len(SpaceGroupList), len(hset))
         return
 
+    def test_spacegroup_representation(self):
+        """Verify SpaceGroup.__repr__()."""
+        numbers = [1, 3, 16, 75, 143, 168, 229]
+        short_names = ["P1", "P2", "P222", "P4", "P3", "P6", "Im-3m"]
+        systems = [
+            "Triclinic",
+            "Monoclinic",
+            "Orthorhombic",
+            "Tetragonal",
+            "Trigonal",
+            "Hexagonal",
+            "Cubic",
+        ]
+        n_symmetry_matrices = [1, 2, 4, 4, 3, 6, 96]
+        n_point_symmetry_matrices = [1, 2, 4, 4, 3, 6, 48]
+        sg_dict = dict(zip(
+            numbers,
+            zip(short_names, systems, n_symmetry_matrices, n_point_symmetry_matrices)
+        ))
+        for key, value in sg_dict.items():
+            sg = GetSpaceGroup(key)
+            expected_str = (
+                               "SpaceGroup #%i (%s, %s). Symmetry matrices: %i, "
+                               "point sym. matr.: %i"
+                           ) % ((key,) + value)
+
+            self.assertEqual(sg.__repr__(), expected_str)
+
+
 # End of class TestRoutines
 
 # ----------------------------------------------------------------------------