Dates

Get current date

import datetime as dt

date = dt.datetime.now()

Date format Conversion

In this section we’ll consider the following date formats:

datetime.datetime
numpy.datetime64
Julian Day: Number of decimal day elapsed since a reference date (often 1950, 1970 or 2000)
(Days, Seconds, Microseconds): elapsed since a reference date (often 1950, 1970 or 2000)
Unix epoch / Unix time / POSIX time / Unix timestamp: Number of seconds elapsed since January 1, 1970 (midnight UTC/GMT)

datetime.datetime and numpy.datetime64

import datetime as dt
import numpy as np

def dt64_to_dt(date: np.datetime64) -> dt.datetime:
    return date.astype('M8[ms]').astype('O')

def dt_to_dt64(date: dt.datetime) -> np.datetime64:
    return np.datetime64(date)

Julian Day and (Days, Seconds, Microseconds)

from typing import Tuple

JulianDay = float
DaySecUsec = Tuple[int, int, int]

def daysecusec_to_jd(date:DaySecUsec) -> JulianDay:
    jdays = float(date[0])
    jdays += (date[1] / 86400.0)
    jdays += (date[2] / (86400.0 * 1e6))
    return jdays

def jd_to_daysecusec(date:JulianDay) -> DaySecUsec:
    us_per_day = 24 * 3600 * 1e6
    julian_day_us = date * us_per_day
    nbdays = int(date)
    julian_day_us -= (nbdays * us_per_day)
    nbseconds = int(julian_day_us / 1e6)
    julian_day_us -= (nbseconds * 1e6)
    nbmicroseconds = int(julian_day_us)
    time_tuple = (nbdays, nbseconds, nbmicroseconds)
    return time_tuple

datetime.datetime and (Days, Seconds, Microseconds)

import datetime as dt
from typing import Tuple

DaySecUsec = Tuple[int, int, int]

def daysecusec_to_dt(date:DaySecUsec, ref_date:dt.datetime=dt.datetime(1950, 1, 1)) -> dt.datetime:
    dt_obj = ref_date
    dt_obj += dt.timedelta(days=date[0])
    dt_obj += dt.timedelta(seconds=date[1])
    dt_obj += dt.timedelta(microseconds=date[2])
    return dt_obj

def dt_to_daysecusec(date:dt.datetime, ref_date:dt.datetime=dt.datetime(1950, 1, 1)) -> DaySecUsec:
    delta = date - ref_date
    time_tuple = (delta.days, delta.seconds, delta.microseconds)
    return time_tuple

numpy.datetime64 and (Days, Seconds, Microseconds)

import numpy as np
from typing import Tuple

DaySecUsec = Tuple[int, int, int]

def daysecusec_to_dt64(date:DaySecUsec, ref_date:np.datetime64=np.datetime64('1950')) -> np.datetime64:
    dt64_obj = ref_date
    dt64_obj += np.timedelta64(date[0], 'D')
    dt64_obj += np.timedelta64(date[1], 's')
    dt64_obj += np.timedelta64(date[2], 'us')
    return dt64_obj

def dt64_to_daysecusec(date:np.datetime64, ref_date:np.datetime64=np.datetime64('1950')) -> DaySecUsec:
    delta = date - ref_date.astype("datetime64[us]")
    nbdays = int(delta / np.timedelta64(1, 'D'))
    delta = delta - np.timedelta64(nbdays, 'D')
    nbseconds = int(delta / np.timedelta64(1, 's'))
    delta = delta - np.timedelta64(nbseconds, 's')
    nbmicroseconds = int(delta / np.timedelta64(1, 'us'))
    time_tuple = (nbdays, nbseconds, nbmicroseconds)
    return time_tuple

datetime.datetime and Julian Days

import datetime as dt

JulianDay = float

def jd_to_dt(date:JulianDay, ref_date:dt.datetime=dt.datetime(1950, 1, 1)) -> dt.datetime:
    return ref_date + dt.timedelta(days=date)

def dt_to_jd(date:dt.datetime, ref_date:dt.datetime=dt.datetime(1950, 1, 1)) -> JulianDay:
    delta = date - ref_date
    jd = delta.days + (delta.seconds + (delta.microseconds / 1e6)) / 86400
    return jd

Unix Timestamp and datetime.datetime

import datetime as dt

UnixTs = float

def unixts_to_dt(date:UnixTs) -> dt.datetime:
    return dt.datetime.utcfromtimestamp(float(date))


def dt_to_unixts(date:dt.datetime) -> UnixTs:
    dt_diff_obj = date - dt.datetime.utcfromtimestamp(0)
    secs = dt_diff_obj.total_seconds()
    return secs