python argparser customized duration type

argparse_duration_to_seconds.py

def duration_to_seconds(duration: str):
    """convert duration string to seconds"""
    unit_to_seconds = {
        "ns": 1e-9,
        "µs": 1e-6,
        "ms": 1e-3,
        "s": 1,
        "m": 60,
        "h": 3600,
    }
    unit = "".join(char for char in duration if char.isalpha()).lower()
    value = float(duration.rstrip(unit))

    if unit not in unit_to_seconds or not duration.endswith(unit):
        raise ValueError(f"cannot parse {duration} as time duration")
    return value * unit_to_seconds[unit]