- Switched from yapf to black
- Reconfigure isort for black
- Resolve black/pylint idiosyncrasies
Note: I used `--experimental-string-processing` because black was
producing "implicit string concatenation", similar to what described
here: https://github.com/psf/black/issues/1837. While currently this
feature is experimental, it will be enabled by default:
https://github.com/psf/black/issues/2188. After running black with the
new string processing so that the generated code merges these `"hello" "
world"` strings concatenations, then I removed
`--experimental-string-processing` for stability, and regenerated the
code again.
To the reviewer: don't even try to open "Files Changed" tab 😄 It's
better to review commit-by-commit, and ignore `run black and isort`.
### Description
Fix https://github.com/grpc/grpc/issues/24470.
Adding one example which demonstrate the following use cases:
* Generate RPC ID on client side and propagate to server.
* Context propagation from client to server.
* Context propagation between different server interceptors and the
server handler.
## Use:
1. Start server: `python3 -m async_greeter_server_with_interceptor`
2. Start client: `python3 -m async_greeter_client`
### Expected Logs:
* On client side:
```
Sending request with rpc id: 73bb98beff10c2dd7b9f2252a1e2039e
Greeter client received: Hello, you!
```
* On server side:
```
INFO:root:Starting server on [::]:50051
INFO:root:Interceptor1 called with rpc_id: default
INFO:root:Interceptor2 called with rpc_id: Interceptor1-default
INFO:root:Handle rpc with id Interceptor2-Interceptor1-73bb98beff10c2dd7b9f2252a1e2039e in server handler.
```
