batch: use builtin next() and catch StopIteration (#38781)

Catching StopIteration is for 3.7 compatibility:
https://www.python.org/dev/peps/pep-0479/

passerelle/utils/__init__.py

@@ -355,7 +355,10 @@ def batch(iterable, size):
         batchiter = islice(sourceiter, size)
         # call next() at least one time to advance, if the caller does not
         # consume the returned iterators, sourceiter will never be exhausted.
-        yield chain([batchiter.next()], batchiter)
+        try:
+            yield chain([next(batchiter)], batchiter)
+        except StopIteration:
+            return
 
 # legacy import, other modules keep importing to_json from passerelle.utils
 from .jsonresponse import to_json

tests/test_utils_batch.py

@@ -0,0 +1,7 @@
+from passerelle.utils import batch
+
+
+def test_batch():
+    data = range(10)
+    for i, d in enumerate(batch(data, 1)):
+        assert list(d) == [i]