next nice datetime

#!/usr/bin/env python3
import datetime


def next_nice_datetime(dt, tzinfo=None):
    tzinfo = datetime.timezone.utc if dt.tzinfo == datetime.timezone.utc else tzinfo
    if dt.minute == 0 and dt.second == 0 and dt.microsecond == 0 and dt.hour in [
            2, 10, 18
    ]:
        return dt.replace(tzinfo=tzinfo)
    elif 18 <= dt.hour:
        return (dt + datetime.timedelta(days=1)).replace(
            hour=2, minute=0, second=0, microsecond=0, tzinfo=tzinfo)
    elif 10 <= dt.hour:
        return dt.replace(
            hour=18, minute=0, second=0, microsecond=0, tzinfo=tzinfo)
    elif 2 <= dt.hour:
        return dt.replace(
            hour=10, minute=0, second=0, microsecond=0, tzinfo=tzinfo)
    else:
        return dt.replace(
            hour=2, minute=0, second=0, microsecond=0, tzinfo=tzinfo)


for t1, t2 in [(dt, next_nice_datetime(dt)) for dt in [
        datetime.datetime.utcnow(),
        datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
        datetime.datetime.strptime('20181221T020000.000000',
                                   '%Y%m%dT%H%M%S.%f'),
        datetime.datetime.strptime('20181221T020000.000001',
                                   '%Y%m%dT%H%M%S.%f')
]]:
    print('{} ---> {}'.format(t1, t2))

d = datetime.datetime.utcnow()
print('{} ---> {}'.format(d, next_nice_datetime(
    d, tzinfo=datetime.timezone.utc)))

for t1, t2 in [(dt, next_nice_datetime(dt)) for dt in [
        datetime.datetime.strptime('20181221T{:02d}0123.456789'.format(s),
                                   '%Y%m%dT%H%M%S.%f') for s in range(24)
]]:
    print('{} ---> {}'.format(t1, t2))