New pattern for async view classes

[simonw]

Refs #878 - starting out with the new AsyncBase class implementing a pytest-inspired asyncio parallel execution mechanism.

[simonw]

I've decided to make the clever asyncio dependency injection opt-in - so you can either decorate with @inject or you can set inject_all = True on the class - for example:

import asyncio
from datasette.utils.asyncdi import AsyncBase, inject


class Simple(AsyncBase):
    def __init__(self):
        self.log = []

    @inject
    async def two(self):
        self.log.append("two")

    @inject
    async def one(self, two):
        self.log.append("one")
        return self.log

    async def not_inject(self, one, two):
        return one + two


class Complex(AsyncBase):
    inject_all = True

    def __init__(self):
        self.log = []

    async def b(self):
        self.log.append("b")

    async def a(self, b):
        self.log.append("a")

    async def go(self, a):
        self.log.append("go")
        return self.log

[codecov]

Codecov Report

Merging #1512 (8f757da) into main (0156c6b) will decrease coverage by 2.10%.
The diff coverage is 36.20%.

@@            Coverage Diff             @@
##             main    #1512      +/-   ##
==========================================
- Coverage   91.82%   89.72%   -2.11%     
==========================================
  Files          34       36       +2     
  Lines        4430     4604     +174     
==========================================
+ Hits         4068     4131      +63     
- Misses        362      473     +111     

Impacted Files	Coverage Δ
datasette/utils/vendored_graphlib.py	0.00% <0.00%> (ø)
datasette/utils/asyncdi.py	96.92% <96.92%> (ø)

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[simonw]

E     File "/home/runner/work/datasette/datasette/datasette/utils/vendored_graphlib.py", line 56
E       if (result := self._node2info.get(node)) is None:
E                  ^
E   SyntaxError: invalid syntax

Oh no - the vendored code I use has := so doesn't work on Python 3.6! Will have to backport it more thoroughly.

[simonw]

I made the changes locally and tested them with Python 3.6 like so:

cd /tmp
mkdir v
cd v
pipenv shell --python=python3.6
cd ~/Dropbox/Development/datasette
pip install -e '.[test]'
pytest tests/test_asyncdi.py

[simonw]

I'm going to extract out the asyncinject stuff into a separate library.

[simonw]

https://github.com/simonw/asyncinject version 0.1a0 is now live on PyPI: https://pypi.org/project/asyncinject/

[simonw]

Closing this PR because I shipped the code in it as a separate library instead.