Python time duration as in golang

duration.py

import re
import time
from datetime import datetime, timedelta


class DurationUnits:
    Nanosecond = 1
    Microsecond = 1000 * Nanosecond
    Millisecond = 1000 * Microsecond
    Second = 1000 * Millisecond
    Minute = 60 * Second
    Hour = 60 * Minute


class Duration:
    unitMap = dict(
        ns=DurationUnits.Nanosecond,
        us=DurationUnits.Microsecond,
        # µs=DurationUnits.Microsecond,  # U+00B5 = micro symbol
        # μs=1000000,  # U+03BC = Greek letter mu
        ms=DurationUnits.Millisecond,
        s=DurationUnits.Second,
        m=DurationUnits.Minute,
        h=DurationUnits.Hour,
    )

    @classmethod
    def parse_duration(cls, s: str):
        n = int(0)
        sign = '+'
        if s[0] == '+' or s[0] == '-':
            sign, s = s[0], s[1:]
        while len(s):
            m = re.match(r"([0-9]+(\.[0-9]+)?)([^0-9]+)", s)
            unit = cls.unitMap.get(m.groups()[2], None)
            if unit is None:
                raise Exception("Missing unit: " + s)
            n += int(unit * float(m.groups()[0]))
            s = s[len(m.groups()[0]) + len(m.groups()[2]):]
        if sign == '-':
            n *= -1
        return cls(n)

    def __str__(self):
        spec = []
        n, neg = abs(self.n), self.n < 0
        for u in reversed([u for u in self.unitMap]):
            m = n // self.unitMap[u]
            if m > 0:
                spec.append(str(m) + str(u))
            n -= int(self.unitMap[u] * (n // self.unitMap[u]))
        if neg:
            return '-' + ''.join(spec)
        return '+' + ''.join(spec)

    def __init__(self, n: int):
        self.n = n

    @property
    def nanoseconds(self):
        return int(self.n)

    @property
    def microseconds(self):
        return int(self.n / self.unitMap['us'])

    @property
    def milliseconds(self):
        return int(self.n / self.unitMap['ms'])

    @property
    def seconds(self):
        return int(self.n / self.unitMap['s'])

    @property
    def minutes(self):
        return int(self.n / self.unitMap['m'])

    @property
    def hours(self):
        return int(self.n / self.unitMap['h'])

    def sleep(self):
        time.sleep(int(self.n / self.unitMap['s']))

    def timedelta(self) -> timedelta:
        return timedelta(microseconds=self.microseconds)

    def add(self, dt: datetime) -> datetime:
        return dt + self.timedelta()

    def sub(self, dt: datetime) -> datetime:
        return dt - self.timedelta()