use simplified implementation of function; change test name to be more descriptive

2 files changed, 11 insertions, 5 deletions

diff --git a/rdflib/plugins/sparql/operators.py b/rdflib/plugins/sparql/operators.py
index c3caab71..18b96658 100644
--- a/rdflib/plugins/sparql/operators.py
+++ b/rdflib/plugins/sparql/operators.py
@@ -612,11 +612,17 @@ def custom_function(uri, override=False, raw=False):
     return decorator
 
 
-def unregister_custom_function(uri, func):
-    if _CUSTOM_FUNCTIONS.get(uri, (None, None))[0] != func:
-        warnings.warn("This function is not registered as %s" % uri.n3())
-    else:
+def unregister_custom_function(uri, func=None):
+    """
+    The 'func' argument is included for compatibility with existing code.
+    A previous implementation checked that the function associated with
+    the given uri was actually 'func', but this is not necessary as the
+    uri should uniquely identify the function.
+    """
+    if _CUSTOM_FUNCTIONS.get(uri):
         del _CUSTOM_FUNCTIONS[uri]
+    else:
+        warnings.warn("This function is not registered as %s" % uri.n3())
 
 
 def Function(e, ctx):
diff --git a/test/test_issue274.py b/test/test_issue274.py
index 38138d8d..fd2b3e14 100644
--- a/test/test_issue274.py
+++ b/test/test_issue274.py
@@ -187,7 +187,7 @@ class TestCustom(TestCase):
     def test_register_override(self):
         register_custom_function(EX.f, self.f, override=True)
 
-    def test_wrong_unregister_fails(self):
+    def test_wrong_unregister_warns(self):
         with pytest.warns(UserWarning):
             unregister_custom_function(EX.f, lambda x, y: None)