ciso8601 2.3.1

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, 3.12.

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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 3.12	Python 3.11	Python 3.10	Python 3.9	Relative slowdown (versus ciso8601, latest Python)	…	Python 3.8	Python 3.7	Python 2.7
ciso8601	98 nsec	90 nsec	122 nsec	122 nsec	N/A	…	118 nsec	124 nsec	134 nsec
backports.datetime_fromisoformat	N/A	N/A	112 nsec	108 nsec	0.9x	…	106 nsec	118 nsec	N/A
datetime (builtin)	129 nsec	132 nsec	N/A	N/A	1.3x	…	N/A	N/A	N/A
pendulum	N/A	180 nsec	187 nsec	186 nsec	2.0x	…	196 nsec	200 nsec	8.52 usec
udatetime	695 nsec	662 nsec	674 nsec	692 nsec	7.1x	…	724 nsec	713 nsec	586 nsec
str2date	6.86 usec	5.78 usec	6.59 usec	6.4 usec	70.0x	…	6.66 usec	6.96 usec	❌
iso8601utils	N/A	N/A	N/A	8.59 usec	70.5x	…	8.6 usec	9.59 usec	11.2 usec
iso8601	10 usec	8.24 usec	8.96 usec	9.21 usec	102.2x	…	9.14 usec	9.63 usec	25.7 usec
isodate	11.1 usec	8.76 usec	10.2 usec	9.76 usec	113.6x	…	9.92 usec	11 usec	44.1 usec
PySO8601	17.2 usec	13.6 usec	16 usec	15.8 usec	175.3x	…	16.1 usec	17.1 usec	17.7 usec
aniso8601	22.2 usec	17.8 usec	23.2 usec	23.1 usec	227.0x	…	24.3 usec	27.2 usec	30.7 usec
zulu	23.3 usec	19 usec	22 usec	21.3 usec	237.9x	…	21.6 usec	22.7 usec	N/A
maya	N/A	36.1 usec	42.5 usec	42.7 usec	401.6x	…	41.3 usec	44.2 usec	N/A
python-dateutil	57.6 usec	51.4 usec	63.3 usec	62.6 usec	587.7x	…	63.7 usec	67.3 usec	119 usec
arrow	62 usec	54 usec	65.5 usec	65.7 usec	633.0x	…	66.6 usec	70.2 usec	78.8 usec
metomi-isodatetime	1.29 msec	1.33 msec	1.76 msec	1.77 msec	13201.1x	…	1.79 msec	1.91 msec	N/A
moment	1.81 msec	1.65 msec	1.75 msec	1.79 msec	18474.8x	…	1.78 msec	1.84 msec	N/A

ciso8601 takes 98 nsec, which is 1.3x faster than datetime (builtin), the next fastest Python 3.12 parser in this comparison.

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

Module	Python 3.12	Python 3.11	Python 3.10	Python 3.9	Relative slowdown (versus ciso8601, latest Python)	…	Python 3.8	Python 3.7	Python 2.7
ciso8601	95 nsec	96.8 nsec	128 nsec	123 nsec	N/A	…	125 nsec	125 nsec	140 nsec
backports.datetime_fromisoformat	N/A	N/A	147 nsec	149 nsec	1.1x	…	138 nsec	149 nsec	N/A
datetime (builtin)	198 nsec	207 nsec	N/A	N/A	2.1x	…	N/A	N/A	N/A
pendulum	N/A	225 nsec	214 nsec	211 nsec	2.3x	…	219 nsec	224 nsec	13.5 usec
udatetime	799 nsec	803 nsec	805 nsec	830 nsec	8.4x	…	827 nsec	805 nsec	768 nsec
str2date	7.73 usec	6.75 usec	7.78 usec	7.8 usec	81.4x	…	7.74 usec	8.13 usec	❌
iso8601	13.7 usec	11.3 usec	12.7 usec	12.5 usec	143.8x	…	12.4 usec	12.6 usec	31.1 usec
isodate	13.7 usec	11.3 usec	12.9 usec	12.7 usec	144.0x	…	12.7 usec	13.9 usec	46.7 usec
iso8601utils	N/A	N/A	N/A	21.4 usec	174.9x	…	22.1 usec	23.4 usec	28.3 usec
PySO8601	25.1 usec	20.4 usec	23.2 usec	23.8 usec	263.8x	…	23.5 usec	24.8 usec	25.3 usec
zulu	26.3 usec	21.4 usec	25.7 usec	24 usec	277.2x	…	24.5 usec	25.3 usec	N/A
aniso8601	27.7 usec	23.7 usec	30.3 usec	30 usec	291.3x	…	31.6 usec	33.8 usec	39.2 usec
maya	N/A	36 usec	41.3 usec	41.8 usec	372.0x	…	42.4 usec	42.7 usec	N/A
python-dateutil	70.7 usec	65.1 usec	77.9 usec	80.2 usec	744.0x	…	79.4 usec	83.6 usec	100 usec
arrow	73 usec	62.8 usec	74.5 usec	73.9 usec	768.6x	…	75.1 usec	80 usec	148 usec
metomi-isodatetime	1.22 msec	1.25 msec	1.72 msec	1.72 msec	12876.3x	…	1.76 msec	1.83 msec	N/A
moment	❌	❌	❌	❌	2305822.8x	…	❌	❌	N/A

ciso8601 takes 95 nsec, which is 2.1x faster than datetime (builtin), the next fastest Python 3.12 parser in this comparison.

Tested on Linux 5.15.49-linuxkit using the following modules:

aniso8601==9.0.1
arrow==1.3.0 (on Python 3.8, 3.9, 3.10, 3.11, 3.12), arrow==1.2.3 (on Python 3.7), arrow==0.17.0 (on Python 2.7)
backports.datetime_fromisoformat==2.0.1
ciso8601==2.3.0
iso8601==2.1.0 (on Python 3.8, 3.9, 3.10, 3.11, 3.12), iso8601==0.1.16 (on Python 2.7)
iso8601utils==0.1.2
isodate==0.6.1
maya==0.6.1
metomi-isodatetime==1!3.1.0
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.