It is that simple. You can pass arguments to `bash -c` with no problems(just don't forget a dummy $0). If you don't want exception spam, replace `check=True` with explicit exit. Here you go, it's 5 lines now.

    #!/usr/bin/env python3
    import sys
    import subprocess
    result = subprocess.run(["bash", "-c", """
    echo I am in bash, I have $# args, arg1 is "$1"
    set -x
    "$@"
    """, "dummy.sh"] + sys.argv[1:])
    sys.exit(result.returncode)

    subprocess.run(["bash", "-c", f"rsync {shlex.quote(filename)} somehost: | some-script"])

The bash syntax highlighting will disappear, correct, and that is a downside. But hey, you are supposed to be rewriting this in python, so it's just more motivation :)