Merge pull request #1659 from gtfierro/fix-issue-1492

Make unregister_custom_function idempotent

2 files changed, 16 insertions, 7 deletions

diff --git a/rdflib/plugins/sparql/operators.py b/rdflib/plugins/sparql/operators.py
index f1c3c1dc..18b96658 100644
--- a/rdflib/plugins/sparql/operators.py
+++ b/rdflib/plugins/sparql/operators.py
@@ -13,6 +13,7 @@ import random
 import uuid
 import hashlib
 import datetime as py_datetime  # naming conflict with function within this module
+import warnings
 
 from functools import reduce
 
@@ -611,10 +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:
-        raise ValueError("This function is not registered as %s" % uri.n3())
-    del _CUSTOM_FUNCTIONS[uri]
+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 248b495c..6a139735 100644
--- a/test/test_issue274.py
+++ b/test/test_issue274.py
@@ -1,5 +1,6 @@
 from .testutils import eq_
 from unittest import TestCase
+import pytest
 
 from rdflib import BNode, Graph, Literal, Namespace, RDFS, XSD
 from rdflib.plugins.sparql.operators import (
@@ -186,9 +187,9 @@ class TestCustom(TestCase):
     def test_register_override(self):
         register_custom_function(EX.f, self.f, override=True)
 
-    def test_wrong_unregister_fails(self):
-        with self.assertRaises(ValueError):
-            unregister_custom_function(EX.f, lambda x, y: None)
+    def test_wrong_unregister_warns(self):
+        with pytest.warns(UserWarning):
+            unregister_custom_function(EX.notexist)
 
     def test_f(self):
         res = query("""SELECT (ex:f(42, "hello") as ?x) {}""")