Convert between duration strings and Python timedelta objects

deltize.py

import re
from datetime import timedelta

format_specs = {
    "y": 31536000,
    "w": 604800,
    "d": 86400,
    "h": 3600,
    "m": 60,
    "s": 1,
}

format_splitter = re.compile(r"([ydhms])")


def to_timedelta(duration: str) -> timedelta:
    parts = format_splitter.split(duration.lower().strip())
    seconds = 0
    for pair in zip(parts[::2], parts[1::2]):
        if pair:
            seconds += int(pair[0]) * format_specs[pair[1]]
    return timedelta(seconds=seconds)


def to_duration(delta: timedelta) -> str:
    seconds = delta.total_seconds()
    duration = []
    for fmt, sec in format_specs.items():
        num = int(seconds // sec)
        if num > 0:
            duration.append("{}{}".format(num, fmt))
            seconds -= num * sec
    return "".join(duration)