fixed SPARQL evaluate issue with StopIteration in py3.7

Author: gromgull

rdflib/plugins/sparql/evaluate.py

@@ -15,6 +15,7 @@
 """
 
 import collections
+import itertools
 
 from rdflib import Variable, Graph, BNode, URIRef, Literal
 from six import iteritems, itervalues
@@ -321,22 +322,9 @@ def evalOrderBy(ctx, part):
 
 
 def evalSlice(ctx, slice):
-    # import pdb; pdb.set_trace()
     res = evalPart(ctx, slice.p)
-    i = 0
-    while i < slice.start:
-        next(res)
-        i += 1
-    i = 0
-    for x in res:
-        i += 1
-        if slice.length is None:
-            yield x
-        else:
-            if i <= slice.length:
-                yield x
-            else:
-                break
+
+    return itertools.islice(res, slice.start, slice.start+slice.length if slice.length is not None else None)
 
 
 def evalReduced(ctx, part):

rdflib/query.py

@@ -3,6 +3,7 @@
 from __future__ import print_function
 
 import os
+import itertools
 import shutil
 import tempfile
 import warnings
@@ -185,7 +186,7 @@ def _get_bindings(self):
         return self._bindings
 
     def _set_bindings(self, b):
-        if isinstance(b, types.GeneratorType):
+        if isinstance(b, (types.GeneratorType, itertools.islice)):
             self._genbindings = b
             self._bindings = []
         else: