isodatetime

Python ISO8601 (2004)
full-specification parser and data model/manipulation utilities.
Intended to be used in a similar way to Python’s datetime module.

Installation

Install from PyPI:

$ pip install metomi-isodatetime

Or with conda: see https://github.com/conda-forge/metomi-isodatetime-feedstock

Usage

Python API:

>>> import metomi.isodatetime.parsers as parse
>>> import metomi.isodatetime.dumpers as dump

# Dates and times
>>> date_time = parse.TimePointParser().parse('2000-01-01T00:00Z')
>>> date_time.month_of_year
1

# Durations
>>> duration = parse.DurationParser().parse('P1YT3H')
>>> duration.get_days_and_seconds()
(365.0, 10800.0)
>>> date_time + duration
<metomi.isodatetime.data.TimePoint: 2001-01-01T03:00:00Z>

# Recurrences
>>> recurrence = parse.TimeRecurrenceParser().parse('R/1999/P1Y')
>>> recurrence.get_next(date_time)
<metomi.isodatetime.data.TimePoint: 2001-01-01T00:00:00Z>

# Output
>>> dump.TimePointDumper().strftime(date_time, '%d/%M/%Y %H:%M:%S')
'01/00/2000 00:00:00'

CLI:

$ isodatetime
2000-01-01T00:00:00Z
$ isodatetime 1066
1066
$ isodatetime 1066 --offset P1Y
1067
$ isodatetime R/2000/P1Y --max 3
2000-01-01T00:00:00Z
2001-01-01T00:00:00Z
2002-01-01T00:00:00Z

Copyright and Terms of Use

Copyright © 2013-2024 British Crown
(Met Office) & Contributors.

This program is free software: you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the Free
Software Foundation, either version 3 of the License, or (at your option) any
later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along
with this program. If not, see GNU licenses.

ISO 8601

ISO 8601 (2004)
is an international standard for writing down date/time information.

It is the correct, internationally-friendly, computer-sortable way to
numerically represent date/time information.

Good reading material:

• http://www.cl.cam.ac.uk/~mgk25/iso-time.html
• http://www.tondering.dk/claus/calendar.html

Reference material:

• http://www.iso.org/iso/home/standards/iso8601.htm
• http://en.wikipedia.org/wiki/ISO_8601

Dates and times

How do I write the year, month-of-year, and day-of-month down?

Syntax	Example
CCYYMMDD	20151231
CCYY-MM-DD	2015-12-31

How about writing down the year, week-of-year, and day-of-week?

Syntax	Example
CCYYWwwD	2015W534
CCYY-Www-D	2015-W53-4

How about writing down the year and day-of-year?

Syntax	Example
CCYYDDD	2015365
CCYY-DDD	2015-365

How do I write just the year?

Either:
CCYY
or
+XCCYY

+X stands for a plus or minus sign (+ or -), followed by a fixed,
agreed number of expanded year digits (X). For example, if we agree to have
2 expanded year digits, we can represent years from -999999 to +999999
(1000000 BC to 999999 AD). Note that 1 BC is the year 0 in the proleptic
Gregorian calendar used by ISO 8601.

For example, you can write the year 1995 AD as:
1995
or
+001995 (using 2 expanded year digits).

Note: writing just the year where you mean a proper date implies Day 1 of
Month 1 in that year - 1995 implies 1995-01 => 1995-01-01 =>
1995-01-01T00 => 1995-01-01T00:00 => 1995-01-01T00:00:00.

How do I write just the year and month-of-year?

Either:
CCYY-MM
or
+XCCYY-MM (+ standing in here for a + or - sign)

(not allowed: CCYYMM or +XCCYYMM).

How do I write dates past the year 9999 and before 0000?

Syntax	Example (2 expanded year digits)
+XCCYYMMDD	+0020151231
+XCCYY-MM-DD	+002015-12-31
+XCCYYWwwD	+002015W534
+XCCYY-Www-D	+002015-W53-4
+XCCYYDDD	+002015365
+XCCYY-DDD	+002015-365

How do I write down time information by itself?

Syntax	Example
hhmmss	083000
hhmm	0830
hh:mm:ss	17:45:01
hh:mm	17:45
hh	08

How do I write down time information at a date in ISO 8601?

Write the time after the date, separated with a T:

Syntax	Example
CCYYMMDDThhmmss	20151231T063101
CCYY-MM-DDThh:mm:ss	2015-12-31T06:31:01
CCYYWwwDThhmmss	2015W534T063101
CCYY-Www-DThh:mm:ss	2015-W53-4T06:31:01
CCYYDDDThhmmss	2015365T063101
CCYY-DDDThh:mm:ss	2015-365T06:31:01

What about just the hour and minute at a date?

Syntax	Example
CCYYWwwDThhmm	2015W534T0631
CCYY-Www-DThh:mm	2015-W53-4T06:31

What about just the hour at a date?

Syntax	Example
CCYYMMDDThh	20151231T06
CCYY-MM-DDThh	2015-12-31T06

What about decimal parts of the hour or minute or second?

Use a comma or period to delimit the decimal part, and don’t include any
smaller units:

Syntax	Example
CCYYMMDDThh,ii	20151231T06,5
CCYYMMDDThh.ii	20151231T06.5
CCYYMMDDThhmm,nn	20151231T0631,3333
CCYYMMDDThhmm.nn	20151231T0631.3333
CCYYMMDDThhmmss,tt	20151231T063101,25671
CCYYMMDDThhmmss.tt	20151231T063101.25671

How do I specify a time zone?

If the time zone is UTC, use “Z” - otherwise, use a numeric representation
of the hours and minutes difference from UTC.

Note that this difference is (TIMEZONE - UTC) - so longitudes east of 0 tend
to have positive differences, and west of 0 usually have negative differences.

Syntax	Example
CCYYMMDDThhmmssZ	20151231T063101Z
CCYY-MM-DDThh:mm:ssZ	2015-12-31T06:31:01Z
CCYYMMDDThhmmss-hh	20151231T013101-05
CCYY-MM-DDThh:mm:ss-hh	2015-12-31T01:31:01-05
CCYYMMDDThhmmss+hh	20151231T083101+02
CCYY-MM-DDThh:mm:ss+hh	2015-12-31T08:31:01+02
CCYYMMDDThhmmss-hhmm	20151230T203101-1000
CCYY-MM-DDThh:mm:ss-hh:mm	2015-12-30T20:31:01-10:00
CCYYMMDDThhmmss+hhmm	20151231T193101+1300
CCYY-MM-DDThh:mm:ss+hh:mm	2015-12-31T19:31:01+13:00

Durations

How do I write down a certain period of time in X units?

A “P” followed by the number of units (optionally including a decimal part)
followed by a designator to mark the units:

Unit type	Unit designator
years	Y
months	M
weeks	W
days	D
hours	H
minutes	M
seconds	S

If the unit is one of hours, minutes, or seconds, you need a leading “T”
to delimit time from date:

Syntax	Example	Meaning
PnY	P2Y	2 years
PTnM	PT7M	7 minutes (note the ‘T’)
PnM	P10M	10 months
PnDTnH	P5DT6H	5 days and 6 hours
PTn,oH	PT5,5H	5 and a half hours
PTn.oH	PT5.5H	5 and a half hours
PnW	P2W	2 weeks

Combining any other unit with weeks is not allowed. Decimals may only be used
for hours, minutes and seconds.

Note that years and months are “nominal” durations, whose exact length of time
depends on their position in the calendar. E.g., a duration of 1 calendar year
starts on a particular day of a particular month and ends on the same day of
the same month in the following calendar year, and may be different to 365 days
in the Gregorian calendar due to leap years.

Conversely, weeks, days, hours, minutes and seconds are exact units, so
P1W == P7D, P1D == PT24H and PT1H == PT60M etc. are always true.
(Although ISO 8601 specifies that weeks and days are nominal durations, there
is no case where they are not exact in our implementation.)

A supplementary format (which has to be agreed in advance) is to specify a
date-time-like duration (PCCYY-MM-DDThh:mm:ss) where the numbers given for
years, months, days, hours, minutes, and seconds are used literally
(P1995-00-00T00:10:00 = P1995YT10M).

Recurring date-time series

1. Recur with a duration given by the difference between a start date and a subsequent date

Example Syntax	Example	Meaning
R/CCYY/CCYY	R/2010/2014	Repeat every 1461 days (≈ 4 years*), starting at 2010-01-01
R/CCYY-MM/CCYY-DDD	R/2010-01/2012-045	Repeat every 774 days (≈ 2 years and 44 days*), starting at 2010-01-01
Rn/CCYY-Www-D/CCYY-Www-D	R5/2015-W05-2/2015-W07-3	Repeat every 15 days (= 2 weeks and 1 day), five times, starting at 2015-W05-2
Rn/CCYY-MM-DDThh/CCYY-MM-DDThh	R1/1925-02-11T00Z/2027-06-01T00Z	Repeat once at 1925-02-11T00Z (note the end date-time is ignored)

*See the previous section as to why only an approximate equivalent number of
years are given.

2. Recur with a specified duration, starting at a context date-time

(You have to supply the context somewhere else)

Example Syntax	Example	Meaning
R/PnMnDTnM	R/P10M3DT45M	Repeat every 10 months, 3 days, and 45 minutes from a context start date-time.
Rn/PnY	R2/P4Y	Repeat every 4 years, for a total of 2 times, from a context start date-time.

3. Recur with a specified duration starting at a particular date-time

Example Syntax	Example	Meaning
R/CCYYMMDDThhZ/PTnH	R/20201231T00Z/PT12H	Repeat every 12 hours starting at 2020-12-31T00Z
R/CCYY-Www-D/PnW	R/2012-W02-1/P1W	Repeat weekly starting at Monday in the second ISO week of 2012
R/CCYYDDDThhmm/PnD	R/1996291T0630+0100/P2D	Repeat every 2 days starting on the 291st day of 1996 at 06:30, UTC + 1
Rn/CCYY-MM-DDThh:mm/PTnH	R2/19900201T06Z/PT12H	Repeat every 12 hours, for a total of 2 repetitions, starting at 1990-02-01T06Z
Rn/CCYY-Www-D/PnW	R5/2012-W02-1/P1W	Repeat weekly, for a total of 5 repetitions, starting at Monday in the second ISO week of 2012
Rn/CCYYDDDThhmm/PnD	R1/1996291T0630Z/P2D	Repeat once on the 291st day of 1996 at 06:30 (note the duration is ignored)

4. Recur with a specified duration ending at a particular date-time

The starting date-time of the recurrence is calculated from the specified
duration.

Example Syntax	Example	Meaning
R/PTnH/CCYY-MM-DDThhZ	R/PT1H/2012-01-02T00Z	Repeat hourly, ending at 2012-01-02T00Z (therefore repeats on the hour)
R/PnY/CCYY	R/P3Y/2000	Repeat every 3 years, ending at 2000-01-01 (therefore repeats at 00:00 January 1st)
R/PTnS/+XCCYYDDDThhmm	R/PT5s/-002500012T1800	Repeat every 5 seconds, ending on the 12th day in 2501 BC at 18:00 (using 2 expanded year digits)
Rn/PnYTnM/CCYY-MM-DDThhZ	R5/P1YT5M/2012-01-02T00Z	Repeat every year and 5 minutes, five times, ending at 2012-01-02T00Z
Rn/PnM/CCYY-MM	R4/P1M/2000-05	Repeat monthly, four times, ending at 2000-05-01 (therefore repeats on the first of the month)