Add fallback for subclasses with required init args

1 files changed, 12 insertions, 3 deletions

diff --git a/rdflib/graph.py b/rdflib/graph.py
index c354a770..8cbc066d 100644
--- a/rdflib/graph.py
+++ b/rdflib/graph.py
@@ -558,7 +558,10 @@ class Graph(Node):
     def __add__(self, other):
         """Set-theoretic union
            BNode IDs are not changed."""
-        retval = self.__class__()
+        try:
+            retval = self.__class__()
+        except TypeError:
+            retval = Graph()
         for (prefix, uri) in set(list(self.namespaces()) + list(other.namespaces())):
             retval.bind(prefix, uri)
         for x in self:
@@ -570,7 +573,10 @@ class Graph(Node):
     def __mul__(self, other):
         """Set-theoretic intersection.
            BNode IDs are not changed."""
-        retval = self.__class__()
+        try:
+            retval = self.__class__()
+        except TypeError:
+            retval = Graph()
         for x in other:
             if x in self:
                 retval.add(x)
@@ -579,7 +585,10 @@ class Graph(Node):
     def __sub__(self, other):
         """Set-theoretic difference.
            BNode IDs are not changed."""
-        retval = self.__class__()
+        try:
+            retval = self.__class__()
+        except TypeError:
+            retval = Graph()
         for x in self:
             if x not in other:
                 retval.add(x)