Starlette

Added

* Starlette now officially supports Python3.9.
* In `StreamingResponse`, allow custom async iterator such as objects from classes implementing `__aiter__`.
* Allow usage of `functools.partial` async handlers in Python versions 3.6 and 3.7.
* Add 418 I'm A Teapot status code.

Changed

* Create tasks from handler coroutines before sending them to `asyncio.wait`.
* Use `format_exception` instead of `format_tb` in `ServerErrorMiddleware`'s `debug` responses.
* Be more lenient with handler arguments when using the `requires` decorator.

* Revert `Queue(maxsize=1)` fix for `BaseHTTPMiddleware` middleware classes and streaming responses.

* The `StaticFiles` constructor now allows `pathlib.Path` in addition to strings for its `directory` argument.

* Fix high memory usage when using BaseHTTPMiddleware middleware classes and streaming responses.

* Fix 404 errors with `StaticFiles`.

* Add support for `Starlette(lifespan=...)` functions.
* More robust path-traversal check in StaticFiles app.
* Fix WSGI PATH_INFO encoding.
* RedirectResponse now accepts optional background parameter
* Allow path routes to contain regex meta characters
* Treat ASGI HTTP 'body' as an optional key.
* Don't use thread pooling for writing to in-memory upload files.

* Add UUID convertor. 903
* More lenient cookie parsing. 900