add type annotations to StreamingResponse (#1708)

starlette/responses.py

@@ -215,10 +215,18 @@ def __init__(
         self.headers["location"] = quote(str(url), safe=":/%#?=@[]!$&'()*+,;")
 
 
+Content = typing.Union[str, bytes]
+SyncContentStream = typing.Iterator[Content]
+AsyncContentStream = typing.AsyncIterable[Content]
+ContentStream = typing.Union[AsyncContentStream, SyncContentStream]
+
+
 class StreamingResponse(Response):
+    body_iterator: AsyncContentStream
+
     def __init__(
         self,
-        content: typing.Any,
+        content: ContentStream,
         status_code: int = 200,
         headers: typing.Optional[typing.Mapping[str, str]] = None,
         media_type: typing.Optional[str] = None,
@@ -257,7 +265,7 @@ async def stream_response(self, send: Send) -> None:
     async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
         async with anyio.create_task_group() as task_group:
 
-            async def wrap(func: typing.Callable[[], typing.Coroutine]) -> None:
+            async def wrap(func: "typing.Callable[[], typing.Awaitable[None]]") -> None:
                 await func()
                 task_group.cancel_scope.cancel()