Fast ISO8601 date time parser for Python written in C
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README.rst

ciso8601

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 Python 2.7, 3.4, 3.5, 3.6, 3.7.

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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.

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

Date time string with no time zone information:

In [1]: import datetime, aniso8601, iso8601, isodate, dateutil.parser, arrow, ciso8601

In [2]: ds = u'2014-01-09T21:48:00.921000'

In [3]: %timeit ciso8601.parse_datetime(ds)
1000000 loops, best of 3: 204 ns per loop

In [4]: %timeit datetime.datetime.strptime(ds, "%Y-%m-%dT%H:%M:%S.%f")
100000 loops, best of 3: 15 µs per loop

In [5]: %timeit dateutil.parser.parse(ds)
10000 loops, best of 3: 122 µs per loop

In [6]: %timeit aniso8601.parse_datetime(ds)
10000 loops, best of 3: 28.9 µs per loop

In [7]: %timeit iso8601.parse_date(ds)
10000 loops, best of 3: 42 µs per loop

In [8]: %timeit isodate.parse_datetime(ds)
10000 loops, best of 3: 69.4 µs per loop

In [9]: %timeit arrow.get(ds).datetime
10000 loops, best of 3: 87 µs per loop

ciso8601 takes 0.204us, which is 73x faster than datetime's strptime, which is not a full ISO8601 parser. It is 141x faster than aniso8601, the next fastest ISO8601 parser in this comparison.

Date time string with time zone information:

In [1]: import datetime, aniso8601, iso8601, isodate, dateutil.parser, arrow, ciso8601

In [2]: ds = u'2014-01-09T21:48:00.921000+05:30'

In [3]: %timeit ciso8601.parse_datetime(ds)
1000000 loops, best of 3: 525 ns per loop

In [4]: %timeit dateutil.parser.parse(ds)
10000 loops, best of 3: 162 µs per loop

In [5]: %timeit aniso8601.parse_datetime(ds)
10000 loops, best of 3: 36.8 µs per loop

In [6]: %timeit iso8601.parse_date(ds)
10000 loops, best of 3: 53.5 µs per loop

In [7]: %timeit isodate.parse_datetime(ds)
10000 loops, best of 3: 82.6 µs per loop

In [8]: %timeit arrow.get(ds).datetime
10000 loops, best of 3: 104 µs per loop

Even with time zone information, ciso8601 is 70x as fast as aniso8601.

Tested on Python 2.7.10 on macOS 10.12.6 using the following modules:

aniso8601==1.2.1
arrow==0.10.0
ciso8601==1.0.4
iso8601==0.1.12
isodate==0.5.4
python-dateutil==2.6.1

Dependency on pytz (Python 2)

In Python 2, ciso8601 uses the pytz library while parsing timestamps with time zone information. This means that if you wish to parse such timestamps, you must first install pytz:

pip install pytz

Otherwise, ciso8601 will raise an exception when you try to parse a timestamp with time zone information:

In [2]: ciso8601.parse_datetime('2014-12-05T12:30:45.123456-05:30')
Out[2]: ImportError: Cannot parse a timestamp with time zone information without the pytz dependency. Install it with `pip install pytz`.

pytz is intentionally not an explicit dependency of ciso8601. This is because many users use ciso8601 to parse only naive timestamps, and therefore don't need this extra dependency. In Python 3, ciso8601 makes use of the built-in datetime.timezone class instead, so pytz is not necessary.

Supported Subset of ISO 8601

ciso8601 only supports the most common subset of ISO 8601.

Date Formats

The following date formats are supported:

Format Example Supported
YYYY-MM-DD 2018-04-29
YYYY-MM 2018-04
YYYYMMDD 2018-04
--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

Week dates or ordinal dates are not currently supported.

Format Example Supported
YYYY-Www (week date) 2009-W01
YYYYWww (week date) 2009W01
YYYY-Www-D (week date) 2009-W01-1
YYYYWwwD (week date) 2009-W01-1
YYYY-DDD (ordinal date) 1981-095
YYYYDDD (ordinal date) 1981095

Time Formats

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

Consistent with RFC 3339, ciso860 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, ciso860 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 Timezone 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.