2 files changed, 48 insertions, 17 deletions
diff --git a/synapse/util/__init__.py b/synapse/util/__init__.py
index 7856353002..60f0de70f7 100644
--- a/synapse/util/__init__.py
+++ b/synapse/util/__init__.py
@@ -15,7 +15,6 @@
 
 import logging
 import re
-from itertools import islice
 
 import attr
 
@@ -107,22 +106,6 @@ class Clock(object):
                 raise
 
 
-def batch_iter(iterable, size):
-    """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)), ())
-
-
 def log_failure(failure, msg, consumeErrors=True):
     """Creates a function suitable for passing to `Deferred.addErrback` that
     logs any failures that occur.
diff --git a/synapse/util/iterutils.py b/synapse/util/iterutils.py
new file mode 100644
index 0000000000..06faeebe7f
--- /dev/null
+++ b/synapse/util/iterutils.py
@@ -0,0 +1,48 @@
+# -*- 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)), ())
+
+
+ISeq = TypeVar("ISeq", bound=Sequence, covariant=True)
+
+
+def chunk_seq(iseq: ISeq, maxlen: int) -> Iterable[ISeq]:
+    """Split the given sequence into chunks of the given size
+
+    The last chunk may be shorter than the given size.
+
+    If the input is empty, no chunks are returned.
+    """
+    return (iseq[i : i + maxlen] for i in range(0, len(iseq), maxlen))