My goal is to read stdout. It's good to hear `subprocess.run()` is deadlock-safe and I can use it safely. Making the docs explicit about it so that others know it's safe would in my opinion be a good idea as well.

Casual users don't know `run()` it uses `communicate()`, not `wait()`, internally, or even that this would mean it cannot deadlock. The current situation when the docs say that `call()` shouldn't be used with `stdout=PIPE` and that `call(...)` is equivalent to `run(...).returncode` indicates `stdout=PIPE` is unsafe with `run()` as well.

A separate questions is that if `call(...)` is equivalent to `run(...).returncode`, should it also be implemented that way. Based on this discussion it would avoid the problem with `stdout=PIPE` also in that case.