Only generate new uuid if not already a valid one

ontopy/ontology.py

@@ -1113,6 +1113,8 @@ def sync_attributes(  # pylint: disable=too-many-branches
         should be updated.  Valid values are:
           None          not changed
           "uuid"        `name_prefix` followed by a global unique id (UUID).
+                        If the name is already valid accoridng to this standard
+                        it will not be regenerated.
           "sequential"  `name_prefix` followed a sequantial number.
         EMMO conventions imply ``name_policy=='uuid'``.
 
@@ -1167,9 +1169,16 @@ class prefLabel(owlready2.label):
         )
         if name_policy == "uuid":
             for obj in chain:
-                obj.name = name_prefix + str(
-                    uuid.uuid5(uuid.NAMESPACE_DNS, obj.name)
-                )
+                try:
+                    # Passing the following means that the name is valid
+                    # and need not be regenerated.
+                    if not obj.name.startswith(name_prefix):
+                        raise ValueError
+                    uuid.UUID(obj.name.lstrip(name_prefix), version=5)
+                except ValueError:
+                    obj.name = name_prefix + str(
+                        uuid.uuid5(uuid.NAMESPACE_DNS, obj.name)
+                    )
         elif name_policy == "sequential":
             for obj in chain:
                 counter = 0

tests/test_basic.py

@@ -58,6 +58,15 @@ class H2O(emmo.Molecule):
     assert water.name.startswith("onto_")
     # A UUID is 32 chars long + 4 `-` chars = 36 chars
     assert len(water.name) == len(name_prefix) + 36
+    synced_uuid = water.name
+    onto.sync_attributes(name_policy="uuid", name_prefix=name_prefix)
+    assert synced_uuid == water.name
+
+    water.name = water.name[1:]
+    assert water.name.startswith("nto_")
+    onto.sync_attributes(name_policy="uuid", name_prefix=name_prefix)
+    assert synced_uuid != water.name
+    assert water.name.startswith("onto_")
 
 
 def test_sync_reasoner(testonto: "Ontology") -> None: