Added a possibilty to copy the ontology

This is done by saving it in a temporary file and loading it as new.

ontopy/ontology.py

@@ -1939,6 +1939,18 @@ def new_annotation_property(
         """
         return self.new_entity(name, parent, "annotation_property")
 
+    def copy(self):
+        """Return a copy of the ontology."""
+        with tempfile.TemporaryDirectory() as handle:
+            tmpfile = os.path.join(handle, "tmp.owl")
+
+            self.save(
+                tmpfile,
+                squash=True,
+            )
+            ontology = get_ontology(tmpfile).load()
+        return ontology
+
 
 class BlankNode:
     """Represents a blank node.

tests/ontopy_tests/test_copy.py

@@ -0,0 +1,33 @@
+from typing import TYPE_CHECKING
+import pytest
+
+if TYPE_CHECKING:
+    from pathlib import Path
+
+
+def test_copy(testonto: "Ontology", repo_dir: "Path") -> None:
+    """Test adding entities to ontology"""
+
+    from ontopy import get_ontology
+    from ontopy.utils import NoSuchLabelError
+
+    # create new reference to ontology
+    testonto = get_ontology(
+        repo_dir / "tests" / "testonto" / "testonto.ttl"
+    ).load()
+    testonto_ref = testonto
+
+    # add new entity to ontology
+    testonto.new_entity("FantasyClass", testonto.TestClass)
+
+    assert testonto_ref.FantasyClass == testonto.FantasyClass
+
+    # make a copy and check that new entity in original is not in copy
+    testonto_copy = testonto.copy()
+
+    testonto.new_entity("FantasyClass2", testonto_copy.TestClass)
+
+    assert testonto.FantasyClass2
+
+    with pytest.raises(NoSuchLabelError):
+        assert testonto_copy.FantasyClass2