Mercurial > babel > old > mirror
diff 0.9.x/doc/dates.txt @ 263:5b7d3f9f7d74 stable
Create branch for 0.9.x maintenance.
author | cmlenz |
---|---|
date | Mon, 20 Aug 2007 08:34:32 +0000 |
parents | |
children |
line wrap: on
line diff
new file mode 100644 --- /dev/null +++ b/0.9.x/doc/dates.txt @@ -0,0 +1,292 @@ +.. -*- mode: rst; encoding: utf-8 -*- + +=============== +Date Formatting +=============== + + +.. contents:: Contents + :depth: 2 +.. sectnum:: + + +When working with date and time information in Python, you commonly use the +classes ``date``, ``datetime`` and/or ``time`` from the `datetime`_ package. +Babel provides functions for locale-specific formatting of those objects in its +``dates`` module: + +.. _`datetime`: http://docs.python.org/lib/module-datetime.html + +.. code-block:: pycon + + >>> from datetime import date, datetime, time + >>> from babel.dates import format_date, format_datetime, format_time + + >>> d = date(2007, 4, 1) + >>> format_date(d, locale='en') + u'Apr 1, 2007' + >>> format_date(d, locale='de_DE') + u'01.04.2007' + +As this example demonstrates, Babel will automatically choose a date format +that is appropriate for the requested locale. + +The ``format_*()`` functions also accept an optional ``format`` argument, which +allows you to choose between one of four format variations: + + * ``short``, + * ``medium`` (the default), + * ``long``, and + * ``full``. + +For example: + +.. code-block:: pycon + + >>> format_date(d, format='short', locale='en') + u'4/1/07' + >>> format_date(d, format='long', locale='en') + u'April 1, 2007' + >>> format_date(d, format='full', locale='en') + u'Sunday, April 1, 2007' + + +Pattern Syntax +============== + +While Babel makes it simple to use the appropriate date/time format for a given +locale, you can also force it to use custom patterns. Note that Babel uses +different patterns for specifying number and date formats compared to the +Python equivalents (such as ``time.strftime()``), which have mostly been +inherited from C and POSIX. The patterns used in Babel are based on the +`Locale Data Markup Language specification`_ (LDML), which defines them as +follows: + + A date/time pattern is a string of characters, where specific strings of + characters are replaced with date and time data from a calendar when formatting + or used to generate data for a calendar when parsing. […] + + Characters may be used multiple times. For example, if ``y`` is used for the + year, ``yy`` might produce "99", whereas ``yyyy`` produces "1999". For most + numerical fields, the number of characters specifies the field width. For + example, if ``h`` is the hour, ``h`` might produce "5", but ``hh`` produces + "05". For some characters, the count specifies whether an abbreviated or full + form should be used […] + + Two single quotes represent a literal single quote, either inside or outside + single quotes. Text within single quotes is not interpreted in any way (except + for two adjacent single quotes). + +For example: + +.. code-block:: pycon + + >>> d = date(2007, 4, 1) + >>> format_date(d, "EEE, MMM d, ''yy", locale='en') + u"Sun, Apr 1, '07" + >>> format_date(d, "EEEE, d.M.yyyy", locale='de') + u'Sonntag, 1.4.2007' + + >>> t = time(15, 30) + >>> format_time(t, "hh 'o''clock' a", locale='en') + u"03 o'clock PM" + >>> format_time(t, 'H:mm a', locale='de') + u'15:30 nachm.' + + >>> dt = datetime(2007, 4, 1, 15, 30) + >>> format_datetime(dt, "yyyyy.MMMM.dd GGG hh:mm a", locale='en') + u'02007.April.01 AD 03:30 PM' + +The syntax for custom datetime format patterns is described in detail in the +the `Locale Data Markup Language specification`_. The following table is just a +relatively brief overview. + + .. _`Locale Data Markup Language specification`: http://unicode.org/reports/tr35/#Date_Format_Patterns + +Date Fields +----------- + + +----------+--------+--------------------------------------------------------+ + | Field | Symbol | Description | + +==========+========+========================================================+ + | Era | ``G`` | Replaced with the era string for the current date. One | + | | | to three letters for the abbreviated form, four | + | | | lettersfor the long form, five for the narrow form | + +----------+--------+--------------------------------------------------------+ + | Year | ``y`` | Replaced by the year. Normally the length specifies | + | | | the padding, but for two letters it also specifies the | + | | | maximum length. | + | +--------+--------------------------------------------------------+ + | | ``Y`` | Same as ``y`` but uses the ISO year-week calendar. | + | +--------+--------------------------------------------------------+ + | | ``u`` | ?? | + +----------+--------+--------------------------------------------------------+ + | Quarter | ``Q`` | Use one or two for the numerical quarter, three for | + | | | the abbreviation, or four for the full name. | + | +--------+--------------------------------------------------------+ + | | ``q`` | Use one or two for the numerical quarter, three for | + | | | the abbreviation, or four for the full name. | + +----------+--------+--------------------------------------------------------+ + | Month | ``M`` | Use one or two for the numerical month, three for the | + | | | abbreviation, or four for the full name, or five for | + | | | the narrow name. | + | +--------+--------------------------------------------------------+ + | | ``L`` | Use one or two for the numerical month, three for the | + | | | abbreviation, or four for the full name, or 5 for the | + | | | narrow name. | + +----------+--------+--------------------------------------------------------+ + | Week | ``w`` | Week of year. | + | +--------+--------------------------------------------------------+ + | | ``W`` | Week of month. | + +----------+--------+--------------------------------------------------------+ + | Day | ``d`` | Day of month. | + | +--------+--------------------------------------------------------+ + | | ``D`` | Day of year. | + | +--------+--------------------------------------------------------+ + | | ``F`` | Day of week in month. | + | +--------+--------------------------------------------------------+ + | | ``g`` | ?? | + +----------+--------+--------------------------------------------------------+ + | Week day | ``E`` | Day of week. Use one through three letters for the | + | | | short day, or four for the full name, or five for the | + | | | narrow name. | + | +--------+--------------------------------------------------------+ + | | ``e`` | Local day of week. Same as E except adds a numeric | + | | | value that will depend on the local starting day of | + | | | the week, using one or two letters. | + | +--------+--------------------------------------------------------+ + | | ``c`` | ?? | + +----------+--------+--------------------------------------------------------+ + +Time Fields +----------- + + +----------+--------+--------------------------------------------------------+ + | Field | Symbol | Description | + +==========+========+========================================================+ + | Period | ``a`` | AM or PM | + +----------+--------+--------------------------------------------------------+ + | Hour | ``h`` | Hour [1-12]. | + | +--------+--------------------------------------------------------+ + | | ``H`` | Hour [0-23]. | + | +--------+--------------------------------------------------------+ + | | ``K`` | Hour [0-11]. | + | +--------+--------------------------------------------------------+ + | | ``k`` | Hour [1-24]. | + +----------+--------+--------------------------------------------------------+ + | Minute | ``m`` | Use one or two for zero places padding. | + +----------+--------+--------------------------------------------------------+ + | Second | ``s`` | Use one or two for zero places padding. | + | +--------+--------------------------------------------------------+ + | | ``S`` | Fractional second, rounds to the count of letters. | + | +--------+--------------------------------------------------------+ + | | ``A`` | Milliseconds in day. | + +----------+--------+--------------------------------------------------------+ + | Timezone | ``z`` | Use one to three letters for the short timezone or | + | | | four for the full name. | + | +--------+--------------------------------------------------------+ + | | ``Z`` | Use one to three letters for RFC 822, four letters for | + | | | GMT format. | + | +--------+--------------------------------------------------------+ + | | ``v`` | Use one letter for short wall (generic) time, four for | + | | | long wall time. | + | +--------+--------------------------------------------------------+ + | | ``V`` | Same as ``z``, except that timezone abbreviations | + | | | should be used regardless of whether they are in | + | | | common use by the locale. | + +----------+--------+--------------------------------------------------------+ + + +Time-zone Support +================= + +Many of the verbose time formats include the time-zone, but time-zone +information is not by default available for the Python ``datetime`` and +``time`` objects. The standard library includes only the abstract ``tzinfo`` +class, which you need appropriate implementations for to actually use in your +application. Babel includes a ``tzinfo`` implementation for UTC (Universal +Time). + +For real time-zone support, it is strongly recommended that you use the +third-party package `pytz`_, which includes the definitions of practically all +of the time-zones used on the world, as well as important functions for +reliably converting from UTC to local time, and vice versa: + +.. code-block:: pycon + + >>> from datetime import time + >>> from pytz import timezone, utc + >>> dt = datetime(2007, 04, 01, 15, 30, tzinfo=utc) + >>> eastern = timezone('US/Eastern') + >>> format_datetime(dt, 'H:mm Z', tzinfo=eastern, locale='en_US') + u'11:30 -0400' + +The recommended approach to deal with different time-zones in a Python +application is to always use UTC internally, and only convert from/to the users +time-zone when accepting user input and displaying date/time data, respectively. +You can use Babel together with ``pytz`` to apply a time-zone to any +``datetime`` or ``time`` object for display, leaving the original information +unchanged: + +.. code-block:: pycon + + >>> british = timezone('Europe/London') + >>> format_datetime(dt, 'H:mm zzzz', tzinfo=british, locale='en_US') + u'16:30 British Summer Time' + +Here, the given UTC time is adjusted to the "Europe/London" time-zone, and +daylight savings time is taken into account. Daylight savings time is also +applied to ``format_time``, but because the actual date is unknown in that +case, the current day is assumed to determine whether DST or standard time +should be used. + + .. _`pytz`: http://pytz.sourceforge.net/ + + +Localized Time-zone Names +------------------------- + +While the ``Locale`` class provides access to various locale display names +related to time-zones, the process of building a localized name of a time-zone +is actually quite complicated. Babel implements it in separately usable +functions in the ``babel.dates`` module, most importantly the +``get_timezone_name`` function: + +.. code-block:: pycon + + >>> from pytz import timezone + >>> from babel import Locale + >>> from babel.dates import get_timezone_name + + >>> tz = timezone('Europe/Berlin') + >>> get_timezone_name(tz, locale=Locale.parse('pt_PT')) + u'Hor\xe1rio Alemanha' + +You can pass the function either a ``datetime.tzinfo`` object, or a +``datetime.date`` or ``datetime.datetime`` object. If you pass an actual date, +the function will be able to take daylight savings time into account. If you +pass just the time-zone, Babel does not know whether daylight savings time is +in effect, so it uses a generic representation, which is useful for example to +display a list of time-zones to the user. + +.. code-block:: pycon + + >>> from datetime import datetime + + >>> dt = tz.localize(datetime(2007, 8, 15)) + >>> get_timezone_name(dt, locale=Locale.parse('de_DE')) + u'Mitteleurop\xe4ische Sommerzeit' + >>> get_timezone_name(tz, locale=Locale.parse('de_DE')) + u'Deutschland' + + +Parsing Dates +============= + +Babel can also parse date and time information in a locale-sensitive manner: + +.. code-block:: pycon + + >>> from babel.dates import parse_date, parse_datetime, parse_time + +.. note:: Date/time parsing is not properly implemented yet