move batch_iter to a separate module

synapse/util/iterutils.py

@@ -0,0 +1,35 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014-2016 OpenMarket Ltd
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from itertools import islice
+from typing import Iterable, Iterator, Sequence, Tuple, TypeVar
+
+T = TypeVar("T")
+
+
+def batch_iter(iterable: Iterable[T], size: int) -> Iterator[Tuple[T]]:
+    """batch an iterable up into tuples with a maximum size
+
+    Args:
+        iterable (iterable): the iterable to slice
+        size (int): the maximum batch size
+
+    Returns:
+        an iterator over the chunks
+    """
+    # make sure we can deal with iterables like lists too
+    sourceiter = iter(iterable)
+    # call islice until it returns an empty tuple
+    return iter(lambda: tuple(islice(sourceiter, size)), ())