See this Python bug https://bugs.python.org/issue33261. The
iscoroutinefunction doesn't recognise partially wrapped coroutine
functions as coroutine functions - which is problematic as the
coroutines will be called as if they are sync, which results in
un-awaited coroutines.
This allows extensions to override the Flask.ensure_sync method and
have the change apply to blueprints as well. Without this change it is
possible for differing blueprints to have differing ensure_sync
approaches depending on the extension used - which would likely result
in event-loop blocking issues.
This also allows blueprints to have a custom ensure_sync, although
this is a by product rather than an expected use case.
Werkzeug offers a ContextVar replacement for Python < 3.7, however it
doesn't work across asyncio tasks, hence it makes sense to error out
rather than find there are odd bugs.
Note the docs build requires the latest (dev) Werkzeug due to this
change (to import ContextVar from werkzeug.local).
This allows for async functions to be passed to the Flask class
instance, for example as a view function,
@app.route("/")
async def index():
return "Async hello"
this comes with a cost though of poorer performance than using the
sync equivalent.
asgiref is the standard way to run async code within a sync context,
and is used in Django making it a safe and sane choice for this.
This code originates from supporting Python 2.4. Dicts are ordered in
supported Pythons as of 3.6. An OrderedDict could be used to indicate
that order matters, but is not since we don't rely on the implementation
differences.
This code originates from the Python 2.4 supporting version of Flask,
with defaultdicts being added in 2.5. Using defaultdict makes the
intentional usage clearer, and slightly simplifies the code.
This takes a popular API whereby instead of passing the HTTP method as
an argument to route it is instead used as the method name i.e.
@app.route("/", methods=["POST"])
is now writeable as,
@app.post("/")
This is simply syntatic sugar, it doesn't do anything else, but makes
it slightly easier for users.
I've included all the methods that are relevant and aren't auto
generated i.e. not connect, head, options, and trace.
