isodatetime

Python ISO 8601 full-specification parser and data model/manipulation utilities. Intended to be used in a similar way to Python's datetime module.

ISO 8601 Primer

ISO 8601 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

This primer covers some commonly used aspects of the standard.

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
Pn,oY	P5,5Y	5 and a half years
Pn.oY	P5.5Y	5 and a half years
PTnM	PT7M	7 minutes (note the 'T')
PnM	P10M	10 months
PnDTnH	P5DT6H	5 days and 6 hours
PnW	P2W	2 weeks

Combining any other unit with weeks is not allowed.

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, starting at the start date

Example Syntax	Example	Meaning
R/CCYY/CCYY	R/2010/2014	Repeat every 4 years, starting at 2010-01-01.
R/CCYY-MM/CCYY-DDD	R/2010-01/2012-045	Repeat every 2 years and 44 days, starting at 2010-01-01
R5/CCYY-Www-D/CCYY-Www-D	R/2015-W05-2/2015-W07-3	Repeat every 2 weeks and 1 day, five times, starting at 2015-W05-2

2 - Recur with a given 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 given 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	R1/1996291T0630+0100/P2D	Repeat once at the 291st day of 1996 at 06:30, UTC + 1

4 - Recur with a given duration counting back from a particular date-time

Example Syntax	Example	Meaning
R/PTnH/CCYY-MM-DDThhZ	R/PT1H/2012-01-02T00Z	Repeat hourly counting back from 2012-01-02T00Z
R/PnY/CCYY	R/P3Y/2000	Repeat every 3 years counting back from 2000-01-01.
R/PTnS/+XCCYYDDDThhmm	R/PT5s/-002500012T1800	Repeat every 5 seconds counting back from 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 minut counting back from 2012-01-02T00Z
Rn/PnM/CCYY-MM	R4/P1M/2000-05	Repeat monthly, four times, counting back from 2000-05-01.