The main classes are chrono.Date, chrono.Time, and chrono.DateTime, which handles dates, times, and date/times respectively. A range of other classes are also available, which provide the functionality that these classes build upon.
python-chrono does not include any handling of time zones or daylight savings time, but this is planned for a future release.
The following sections describe some typical usage of the chrono.Date class. The chrono.Time and chrono.DateTime classes behave in much the same way, but for simplicity only chrono.Date is covered here.
Dates can be specified using either ISO, US, or european formats. Lists of valid formats are available in the chrono.parser documentation.
By default, python-chrono uses the parser set in chrono.DEFAULT_PARSER - normally chrono.parser.CommonParser, which accepts the most commonly used date formats. The notable exceptions are formats without separators (which for example can be interpreted as either US or european dates), and unusual separators such as . in US dates (which is the standard separator in Europe). In order to parse such formats, you need to either set another default in chrono.DEFAULT_PARSER, or pass the proper parser to chrono.Date.
Date parsing is done simply by instantiating a chrono.Date object, passing the date string to be parsed as input. Once instantiated, the attributes chrono.Date.year, chrono.Date.month, and chrono.Date.day will contain the respective date parts:
.. doctest::
>>> date = chrono.Date("2009-07-23")
>>> date.year
2009
>>> date.month
7
>>> date.day
23
To retrieve all the attributes at once, use chrono.Date.get():
.. doctest::
>>> date = chrono.Date("2009-07-23")
>>> date.get()
(2009, 7, 23)
The default chrono.parser.CommonParser parser handles most normal date formats, such as:
.. doctest::
>>> # ISO dates >>> chrono.Date("2009-07-23").get() (2009, 7, 23)>>> # US dates >>> chrono.Date("07/23/2009").get() (2009, 7, 23)>>> # european dates >>> chrono.Date("23.07.2009").get() (2009, 7, 23)>>> # ISO week dates >>> chrono.Date("2009-W32").get() (2009, 8, 3)>>> # ISO ordinal dates >>> chrono.Date("2009-314").get() (2009, 11, 10)>>> # ISO month dates >>> chrono.Date("2009-07").get() (2009, 7, 1)
In order to parse all valid date formats for a region, you can pass the proper parser class to chrono.Date:
.. doctest::
>>> # US dates with two-digit year and no separator >>> chrono.Date("072309", chrono.parser.USParser).get() (2009, 7, 23)>>> # slash-separated european dates >>> chrono.Date("23/07/2009", chrono.parser.EuroParser).get() (2009, 7, 23)
If chrono.Date is passed an invalid date it will raise either chrono.error.ParseError for invalid/unknown format, or a subclass of chrono.error.DateError (such as chrono.error.MonthError) if the date was parsed properly but contained an invalid date value:
.. doctest::
>>> date = chrono.Date("xyz") Traceback (most recent call last): ParseError: Invalid ISO date value 'xyz'>>> date = chrono.Date("2009-13-27") Traceback (most recent call last): MonthError: Month '13' not in range 1-12
You can also pass a range of non-string inputs to the class, which will be handled according to the object type:
.. doctest::
>>> # boolean True indicates the current date >>> chrono.Date(True).get() # doctest: +SKIP (2010, 1, 23)>>> # integers are interpreted as UNIX timestamps >>> chrono.Date(1263745408).get() (2010, 1, 17)>>> # fetch data from time.struct_time objects >>> chrono.Date(time.localtime()).get() # doctest: +SKIP (2010, 1, 23)>>> # fetch data from datetime.date objects >>> chrono.Date(datetime.date(2010, 7, 23)).get() (2010, 7, 23)
For a complete list of all accepted input types, see the chrono.Date documentation.
To parse date strings without instantiating a chrono.Date object, you can use the parser classes directly:
.. doctest::
>>> # parses all supported ISO date formats >>> chrono.parser.ISOParser.parse_date("2009-07-23") (2009, 7, 23)>>> # only parses week dates >>> chrono.parser.ISOParser.week("2009-W32") (2009, 8, 3)>>> # only parses ordinal dates >>> chrono.parser.ISOParser.ordinal("2009-314") (2009, 11, 10)
See the chrono.parser documentation for more information on parser classes.
python-chrono supports both the ISO and US calendars, which have the following characteristics:
ISO Calendar:
- Weeks start on Monday
- The first week of a year is the week which contains the first Thursday
US Calendar:
- Weeks start on Sunday
- The first week of a year is the week which contains January 1st
By default the calendar set in chrono.DEFAULT_CALENDAR is used, normally chrono.calendar.ISOCalendar. To use another calendar, either set it as the default in chrono.DEFAULT_CALENDAR, or pass the proper calendar to chrono.Date. As can be seen above, this only affects functionality related to week numbers or week days.
chrono.Date has a number of methods for retreiving calendar-related information about about a date, such as:
.. doctest::
>>> # week that contains the date >>> chrono.Date("2009-07-23").week() (2009, 30)>>> # whether the date is in a leap year >>> chrono.Date("2008-07-23").leapyear() True>>> # number of days in the month >>> chrono.Date("2009-07-23").monthdays() 31>>> # weekday of the date >>> chrono.Date("2009-07-23").weekday() 4
To use the US calendar instead, pass the chrono.calendar.USCalendar class to chrono.Date:
.. doctest::
>>> # US week containing date >>> chrono.Date("2009-07-23", calendar=chrono.calendar.USCalendar).week() (2009, 30)>>> # US weekday of the date >>> chrono.Date("2009-07-23", calendar=chrono.calendar.USCalendar).weekday() 5
For a full list of calendar-related methods, see the chrono.Date documentation.
If you would like to retreive calendar information without having to instantiate a chrono.Date object, you can use the underlying calendar class directly:
.. doctest::
>>> chrono.calendar.ISOCalendar.yeardays(2008) 366>>> chrono.calendar.ISOCalendar.ordinal(2009, 7, 23) 204>>> chrono.calendar.ISOCalendar.weekdate(2009, 7, 23) (2009, 30, 4)
See the chrono.calendar documentation for more information.
Date arithmetic (addition, subtraction, etc) is done by special handling of the chrono.Date.year, chrono.Date.month, and chrono.Date.day attributes. If any of these are set to a value that is outside their valid range, the object will automatically update the attributes to a proper date, by incrementing or decrementing values as necessary.
Here are some examples:
.. doctest::
>>> # adding days to a date >>> date = chrono.Date("2009-07-26") >>> date.day += 10 >>> date.get() (2009, 8, 5)>>> # subtracting months from a date >>> date.month -= 2 >>> date.get() (2009, 6, 5)>>> # adding years to a date >>> date.year += 3 >>> date.get() (2012, 6, 5)
Warning
When the date is on one of the last days of a month, and the chrono.Date.month or chrono.Date.year attribute is changed, you may get a result which is in a different month than the one you expect. This happens when the day number is out of range for the new month, due to differences in month lengths:
>>> date = chrono.Date("2009-07-31")
>>> date.month -= 1
>>> date.get()
(2009, 7, 1)
When chrono.Date.month is set to 6, the date will become 2009-06-31. Since June only has 30 days this will trigger the overflow-handling that the date arithmetic relies on, and update the date to a valid date. The same happens with leap years:
>>> date = chrono.Date("2008-02-29")
>>> date.year += 1
>>> date.get()
(2009, 3, 1)
Date formatting is done via the chrono.Date.format() method, which takes a string containing substitution variables of the form $name or ${name}, and replaces them with actual values:
.. doctest::
>>> # full human-readable date >>> chrono.Date("2009-07-23").format("$weekdayname $day. $monthname $year") 'Thursday 23. July 2009'>>> # ISO-date, using 0-padded values >>> chrono.Date("2009-07-23").format("$0year-$0month-$0day") '2009-07-23'
For a full list of substitution variables, see the chrono.formatter.Formatter documentation.
Date comparisons can be done using the normal Python comparison operators: ==, !=, >, and <:
.. doctest::
>>> chrono.Date("2009-07-31") == chrono.Date(year = 2009, month = 7, day = 31) True>>> chrono.Date("2009-07-31") > chrono.Date("2009-07-01") True>>> chrono.Date("2009-07-31") <= chrono.Date("2009-07-01") False
If the value that is being compared with is not a chrono.Date object, it will be converted to one if possible. This allows for comparisons with strings, UNIX timestamps, time.struct_time or datetime.date objects, and any other value that chrono.Date is able to process:
.. doctest::
>>> # string with ISO date >>> chrono.Date("2009-07-31") == "2009-07-31" True>>> # string with ISO weekdate >>> chrono.Date("2009-07-31") != "2009-W31-5" False>>> # integer UNIX timestamp >>> chrono.Date("2009-07-31") > 1241683613 True>>> # time.struct_time, as returned by time.localtime() etc >>> chrono.Date("2009-07-31") > time.localtime() False>>> # datetime.date objects >>> chrono.Date("2009-07-31") >= datetime.date(2009, 2, 17) True