use asyncio.run

[davidism]

Python 3.10 shows a deprecation warning when using asyncio.get_event_loop while not in an event loop, which is the case when running the sync render method for an async template. Use asyncio.run instead, which manages running in an event loop.

generate is no longer particularly useful when called on an async template, as calling run over and over again would create new loops and be inefficient. So it collects the entire render then yields it item by item so that it's still a generator. generate already doesn't seem particularly useful, as only very simple templates without blocks or other internal buffers will actually yield one statement at a time.

I think we should deprecate calling render and generate if the template is async. It's a blocking call in async mode, and it doesn't really make sense to render an async environment from sync code, as you'd have to manage everything manually for that to be useful. It also requires ignoring some type errors. Users should call render_async from a running loop when using an async environment.

• fixes Python 3.10: tests fail due to DeprecationWarning: There is no current event loop #1443

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.