ciso8601 2.3.0

Fast ISO8601 date time parser for Python written in C

ciso8601 converts ISO 8601 or RFC 3339 date time strings into Python datetime objects.

Since it’s written as a C module, it is much faster than other Python libraries. Tested with cPython 2.7, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 3.10, 3.11.

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Contents

• Quick start

• Migration to v2

• When should I not use ciso8601?

• Error handling

• Benchmark

• Supported subset of ISO 8601

  • Date formats

  • Time formats

  • Time zone information

• Strict RFC 3339 parsing

• Ignoring time zone information while parsing

Quick start

% pip install ciso8601

In [1]: import ciso8601

In [2]: ciso8601.parse_datetime('2014-12-05T12:30:45.123456-05:30')
Out[2]: datetime.datetime(2014, 12, 5, 12, 30, 45, 123456, tzinfo=pytz.FixedOffset(330))

In [3]: ciso8601.parse_datetime('20141205T123045')
Out[3]: datetime.datetime(2014, 12, 5, 12, 30, 45)

Migration to v2

Version 2.0.0 of ciso8601 changed the core implementation. This was not entirely backwards compatible, and care should be taken when migrating See CHANGELOG for the Migration Guide.

When should I not use ciso8601?

ciso8601 is not necessarily the best solution for every use case (especially since Python 3.11). See Should I use ciso8601?

Error handling

Starting in v2.0.0, ciso8601 offers strong guarantees when it comes to parsing strings.

parse_datetime(dt: String): datetime is a function that takes a string and either:

• Returns a properly parsed Python datetime, if and only if the entire string conforms to the supported subset of ISO 8601

• Raises a ValueError with a description of the reason why the string doesn’t conform to the supported subset of ISO 8601

If time zone information is provided, an aware datetime object will be returned. Otherwise, a naive datetime is returned.

Benchmark

Parsing a timestamp with no time zone information (e.g., 2014-01-09T21:48:00):

Module	Python 3.11	Python 3.10	Python 3.9	Python 3.8	Python 3.7	Python 2.7	Relative slowdown (versus ciso8601, latest Python)
ciso8601	84.5 nsec	111 nsec	102 nsec	111 nsec	112 nsec	134 nsec	N/A
backports.datetime_fromisoformat	N/A	107 nsec	105 nsec	117 nsec	112 nsec	N/A	1.0x
datetime (builtin)	114 nsec	N/A	N/A	N/A	N/A	N/A	1.4x
pendulum	174 nsec	177 nsec	164 nsec	201 nsec	202 nsec	8.52 usec	2.1x
udatetime	593 nsec	627 nsec	640 nsec	713 nsec	660 nsec	586 nsec	7.0x
str2date	5.32 usec	6.14 usec	5.88 usec	6.68 usec	6.53 usec	Incorrect Result (None)	62.9x
iso8601	7.28 usec	8.32 usec	8.12 usec	9.59 usec	8.78 usec	25.7 usec	86.1x
iso8601utils	N/A	N/A	7.91 usec	9.28 usec	8.81 usec	11.2 usec	77.5x
isodate	8.21 usec	9.5 usec	9.05 usec	10.8 usec	10.5 usec	44.1 usec	97.1x
PySO8601	12.9 usec	14.8 usec	15 usec	17.2 usec	16.3 usec	17.7 usec	152.9x
aniso8601	16.8 usec	22.1 usec	21 usec	23.5 usec	24.7 usec	30.7 usec	198.3x
zulu	18 usec	21.1 usec	20.4 usec	22.1 usec	21.2 usec	N/A	212.5x
maya	35.1 usec	40.7 usec	40.2 usec	40.1 usec	41.8 usec	N/A	415.4x
python-dateutil	49 usec	59 usec	57.4 usec	63 usec	64.3 usec	119 usec	579.6x
arrow	51.5 usec	61.6 usec	60.3 usec	62.8 usec	65.8 usec	78.8 usec	609.7x
metomi-isodatetime	1.18 msec	1.67 msec	1.64 msec	1.73 msec	1.81 msec	N/A	13981.2x
moment	1.57 msec	1.62 msec	1.65 msec	1.7 msec	1.74 msec	N/A	18540.2x

ciso8601 takes 84.5 nsec, which is 1.4x faster than datetime (builtin), the next fastest Python 3.11 parser in this comparison.

Parsing a timestamp with time zone information (e.g., 2014-01-09T21:48:00-05:30):

Module	Python 3.11	Python 3.10	Python 3.9	Python 3.8	Python 3.7	Python 2.7	Relative slowdown (versus ciso8601, latest Python)
ciso8601	115 nsec	116 nsec	109 nsec	111 nsec	115 nsec	140 nsec	N/A
backports.datetime_fromisoformat	N/A	163 nsec	146 nsec	139 nsec	148 nsec	N/A	1.4x
datetime (builtin)	199 nsec	N/A	N/A	N/A	N/A	N/A	1.7x
pendulum	205 nsec	210 nsec	189 nsec	209 nsec	204 nsec	13.5 usec	1.8x
udatetime	745 nsec	719 nsec	731 nsec	726 nsec	734 nsec	768 nsec	6.5x
str2date	6.78 usec	7.55 usec	7.67 usec	7.69 usec	7.47 usec	Incorrect Result (None)	58.8x
iso8601	11.1 usec	12.1 usec	12 usec	12.3 usec	12.2 usec	31.1 usec	96.1x
isodate	11.4 usec	12.4 usec	12.4 usec	13 usec	13.1 usec	46.7 usec	98.8x
iso8601utils	N/A	N/A	20.3 usec	37.8 usec	22.7 usec	28.3 usec	185.5x
PySO8601	20.5 usec	22.9 usec	23.2 usec	23.5 usec	24.8 usec	25.3 usec	178.0x
zulu	25.5 usec	24.2 usec	23.4 usec	23.3 usec	24.3 usec	N/A	221.7x
aniso8601	29.5 usec	28.5 usec	27.6 usec	30.1 usec	32.1 usec	39.2 usec	256.2x
maya	37.1 usec	40.4 usec	38.9 usec	40.3 usec	40.9 usec	N/A	322.0x
arrow	62.7 usec	73 usec	69.9 usec	71.7 usec	75.5 usec	100 usec	544.4x
python-dateutil	64.8 usec	76.6 usec	73.4 usec	77.6 usec	78.5 usec	148 usec	562.3x
metomi-isodatetime	1.22 msec	1.67 msec	1.6 msec	1.6 msec	1.76 msec	N/A	10604.3x
moment	Incorrect Result (None)	Incorrect Result (None)	Incorrect Result (None)	Incorrect Result (None)	Incorrect Result (None)	N/A	1782198.3x

ciso8601 takes 115 nsec, which is 1.7x faster than datetime (builtin), the next fastest Python 3.11 parser in this comparison.

Tested on Linux 5.15.49-linuxkit using the following modules:

aniso8601==9.0.1
arrow==0.17.0 (on Python 2.7), arrow==1.2.3 (on Python 3.7, 3.8, 3.9, 3.10, 3.11)
backports.datetime_fromisoformat==2.0.0
ciso8601==2.3.0
iso8601==0.1.16 (on Python 2.7), iso8601==1.1.0 (on Python 3.7, 3.8, 3.9, 3.10, 3.11)
iso8601utils==0.1.2
isodate==0.6.1
maya==0.6.1
metomi-isodatetime==1!3.0.0
moment==0.12.1
pendulum==2.1.2
PySO8601==0.2.0
python-dateutil==2.8.2
str2date==0.905
udatetime==0.0.17
zulu==2.0.0

For full benchmarking details (or to run the benchmark yourself), see benchmarking/README.rst

Supported subset of ISO 8601

ciso8601 only supports a subset of ISO 8601, but supports a superset of what is supported by Python itself (datetime.fromisoformat), and supports the entirety of the RFC 3339 specification.

Date formats

The following date formats are supported:

Format	Example	Supported
YYYY-MM-DD (extended)	2018-04-29	✅
YYYY-MM (extended)	2018-04	✅
YYYYMMDD (basic)	20180429	✅
YYYY-Www-D (week date)	2009-W01-1	✅
YYYY-Www (week date)	2009-W01	✅
YYYYWwwD (week date)	2009W011	✅
YYYYWww (week date)	2009W01	✅
YYYY-DDD (ordinal date)	1981-095	✅
YYYYDDD (ordinal date)	1981095	✅

Uncommon ISO 8601 date formats are not supported:

Format	Example	Supported
--MM-DD (omitted year)	--04-29	❌
--MMDD (omitted year)	--0429	❌
±YYYYY-MM (>4 digit year)	+10000-04	❌
+YYYY-MM (leading +)	+2018-04	❌
-YYYY-MM (negative -)	-2018-04	❌

Time formats

Times are optional and are separated from the date by the letter T.

Consistent with RFC 3339, ciso8601 also allows either a space character, or a lower-case t, to be used instead of a T.

The following time formats are supported:

Format	Example	Supported
hh	11	✅
hhmm	1130	✅
hh:mm	11:30	✅
hhmmss	113059	✅
hh:mm:ss	11:30:59	✅
hhmmss.ssssss	113059.123456	✅
hh:mm:ss.ssssss	11:30:59.123456	✅
hhmmss,ssssss	113059,123456	✅
hh:mm:ss,ssssss	11:30:59,123456	✅
Midnight (special case)	24:00:00	✅
hh.hhh (fractional hours)	11.5	❌
hh:mm.mmm (fractional minutes)	11:30.5	❌

Note: Python datetime objects only have microsecond precision (6 digits). Any additional precision will be truncated.

Time zone information

Time zone information may be provided in one of the following formats:

Format	Example	Supported
Z	Z	✅
z	z	✅
±hh	+11	✅
±hhmm	+1130	✅
±hh:mm	+11:30	✅

While the ISO 8601 specification allows the use of MINUS SIGN (U+2212) in the time zone separator, ciso8601 only supports the use of the HYPHEN-MINUS (U+002D) character.

Consistent with RFC 3339, ciso8601 also allows a lower-case z to be used instead of a Z.

Strict RFC 3339 parsing

ciso8601 parses ISO 8601 datetimes, which can be thought of as a superset of RFC 3339 (roughly). In cases where you might want strict RFC 3339 parsing, ciso8601 offers a parse_rfc3339 method, which behaves in a similar manner to parse_datetime:

parse_rfc3339(dt: String): datetime is a function that takes a string and either:

• Returns a properly parsed Python datetime, if and only if the entire string conforms to RFC 3339.

• Raises a ValueError with a description of the reason why the string doesn’t conform to RFC 3339.

Ignoring time zone information while parsing

It takes more time to parse timestamps with time zone information, especially if they’re not in UTC. However, there are times when you don’t care about time zone information, and wish to produce naive datetimes instead. For example, if you are certain that your program will only parse timestamps from a single time zone, you might want to strip the time zone information and only output naive datetimes.

In these limited cases, there is a second function provided. parse_datetime_as_naive will ignore any time zone information it finds and, as a result, is faster for timestamps containing time zone information.

In [1]: import ciso8601

In [2]: ciso8601.parse_datetime_as_naive('2014-12-05T12:30:45.123456-05:30')
Out[2]: datetime.datetime(2014, 12, 5, 12, 30, 45, 123456)

NOTE: parse_datetime_as_naive is only useful in the case where your timestamps have time zone information, but you want to ignore it. This is somewhat unusual. If your timestamps don’t have time zone information (i.e. are naive), simply use parse_datetime. It is just as fast.