Moved relay is_node definition

graphene/relay/__init__.py

@@ -1,9 +1,10 @@
-from .node import Node
+from .node import Node, is_node
 from .mutation import ClientIDMutation
 from .connection import Connection, ConnectionField
 
 __all__ = [
     'Node',
+    'is_node',
     'ClientIDMutation',
     'Connection',
     'ConnectionField',

graphene/relay/connection.py

@@ -12,18 +12,11 @@ from ..types.objecttype import ObjectType, ObjectTypeMeta
 from ..types.options import Options
 from ..utils.is_base_type import is_base_type
 from ..utils.props import props
-from .node import Node
+from .node import Node, is_node
 
 from ..types.utils import get_fields_in_type, yank_fields_from_attrs
 
 
-def is_node(objecttype):
-    for i in objecttype._meta.interfaces:
-        if issubclass(i, Node):
-            return True
-    return False
-
-
 class PageInfo(ObjectType):
     has_next_page = Boolean(
         required=True,
@@ -125,8 +118,8 @@ class IterableConnectionField(Field):
         else:
             connection_type = type
         assert issubclass(connection_type, Connection), (
-            '{} type have to be a subclass of Connection'
+            '{} type have to be a subclass of Connection. Received "{}".'
-        ).format(str(self))
+        ).format(str(self), connection_type)
         return connection_type
 
     @staticmethod

graphene/relay/node.py

@@ -7,6 +7,13 @@ from ..types import ObjectType, Interface, ID, Field
 from ..types.interface import InterfaceMeta
 
 
+def is_node(objecttype):
+    for i in objecttype._meta.interfaces:
+        if issubclass(i, Node):
+            return True
+    return False
+
+
 def get_default_connection(cls):
     from .connection import Connection
     assert issubclass(cls, ObjectType), (