diff --git a/synapse/util/iterutils.py b/synapse/util/iterutils.py
index 8ac3eab2f5..4938ddf703 100644
--- a/synapse/util/iterutils.py
+++ b/synapse/util/iterutils.py
@@ -21,13 +21,28 @@ from typing import (
Iterable,
Iterator,
Mapping,
- Sequence,
Set,
+ Sized,
Tuple,
TypeVar,
)
+from typing_extensions import Protocol
+
T = TypeVar("T")
+S = TypeVar("S", bound="_SelfSlice")
+
+
+class _SelfSlice(Sized, Protocol):
+ """A helper protocol that matches types where taking a slice results in the
+ same type being returned.
+
+ This is more specific than `Sequence`, which allows another `Sequence` to be
+ returned.
+ """
+
+ def __getitem__(self: S, i: slice) -> S:
+ ...
def batch_iter(iterable: Iterable[T], size: int) -> Iterator[Tuple[T, ...]]:
@@ -46,7 +61,7 @@ def batch_iter(iterable: Iterable[T], size: int) -> Iterator[Tuple[T, ...]]:
return iter(lambda: tuple(islice(sourceiter, size)), ())
-def chunk_seq(iseq: Sequence[T], maxlen: int) -> Iterable[Sequence[T]]:
+def chunk_seq(iseq: S, maxlen: int) -> Iterator[S]:
"""Split the given sequence into chunks of the given size
The last chunk may be shorter than the given size.
|
