#3142: Improve usability of multi() and multi_future() type annotations

Author: jrheard-seesaw

tornado/gen.py

@@ -91,7 +91,18 @@ def get(self):
     contextvars = None  # type: ignore
 
 import typing
-from typing import Union, Any, Callable, List, Type, Tuple, Awaitable, Dict, overload
+from typing import (
+    Mapping,
+    Union,
+    Any,
+    Callable,
+    List,
+    Type,
+    Tuple,
+    Awaitable,
+    Dict,
+    overload,
+)
 
 if typing.TYPE_CHECKING:
     from typing import Sequence, Deque, Optional, Set, Iterable  # noqa: F401
@@ -426,7 +437,7 @@ def __anext__(self) -> Future:
 
 
 def multi(
-    children: Union[List[_Yieldable], Dict[Any, _Yieldable]],
+    children: Union[Sequence[_Yieldable], Mapping[Any, _Yieldable]],
     quiet_exceptions: "Union[Type[Exception], Tuple[Type[Exception], ...]]" = (),
 ) -> "Union[Future[List], Future[Dict]]":
     """Runs multiple asynchronous operations in parallel.
@@ -480,7 +491,7 @@ def multi(
 
 
 def multi_future(
-    children: Union[List[_Yieldable], Dict[Any, _Yieldable]],
+    children: Union[Sequence[_Yieldable], Mapping[Any, _Yieldable]],
     quiet_exceptions: "Union[Type[Exception], Tuple[Type[Exception], ...]]" = (),
 ) -> "Union[Future[List], Future[Dict]]":
     """Wait for multiple asynchronous futures in parallel.