Two of my colleagues missed the "The arguments shown above are merely the most common ones, ..." caveat on the subprocess.run documentation, and assumed that Python 3.5 only supported the "cwd" option in the low level Popen API, and not any of the higher level APIs.

Something we could potential do is include a "**other_popen_kwargs" placeholder in the affected API signatures (run, call, check_call, check_output) that makes it clear there are more options beyond the explicitly listed ones.