Build a list of flags.

def get_flag_args(**options):
    """Build a list of flags."""
    flags = []
    for key, value in options.items():
        # Build short flags.
        if len(key) == 1:
            flag = f'-{key}'
        # Built long flags.
        else:
            flag = f'--{key}'
        flags = flags + [flag, value]
    return flags