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date Mon, 20 Aug 2007 08:34:32 +0000
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1 .. -*- mode: rst; encoding: utf-8 -*-
2
3 ===============
4 Date Formatting
5 ===============
6
7
8 .. contents:: Contents
9 :depth: 2
10 .. sectnum::
11
12
13 When working with date and time information in Python, you commonly use the
14 classes ``date``, ``datetime`` and/or ``time`` from the `datetime`_ package.
15 Babel provides functions for locale-specific formatting of those objects in its
16 ``dates`` module:
17
18 .. _`datetime`: http://docs.python.org/lib/module-datetime.html
19
20 .. code-block:: pycon
21
22 >>> from datetime import date, datetime, time
23 >>> from babel.dates import format_date, format_datetime, format_time
24
25 >>> d = date(2007, 4, 1)
26 >>> format_date(d, locale='en')
27 u'Apr 1, 2007'
28 >>> format_date(d, locale='de_DE')
29 u'01.04.2007'
30
31 As this example demonstrates, Babel will automatically choose a date format
32 that is appropriate for the requested locale.
33
34 The ``format_*()`` functions also accept an optional ``format`` argument, which
35 allows you to choose between one of four format variations:
36
37 * ``short``,
38 * ``medium`` (the default),
39 * ``long``, and
40 * ``full``.
41
42 For example:
43
44 .. code-block:: pycon
45
46 >>> format_date(d, format='short', locale='en')
47 u'4/1/07'
48 >>> format_date(d, format='long', locale='en')
49 u'April 1, 2007'
50 >>> format_date(d, format='full', locale='en')
51 u'Sunday, April 1, 2007'
52
53
54 Pattern Syntax
55 ==============
56
57 While Babel makes it simple to use the appropriate date/time format for a given
58 locale, you can also force it to use custom patterns. Note that Babel uses
59 different patterns for specifying number and date formats compared to the
60 Python equivalents (such as ``time.strftime()``), which have mostly been
61 inherited from C and POSIX. The patterns used in Babel are based on the
62 `Locale Data Markup Language specification`_ (LDML), which defines them as
63 follows:
64
65 A date/time pattern is a string of characters, where specific strings of
66 characters are replaced with date and time data from a calendar when formatting
67 or used to generate data for a calendar when parsing. […]
68
69 Characters may be used multiple times. For example, if ``y`` is used for the
70 year, ``yy`` might produce "99", whereas ``yyyy`` produces "1999". For most
71 numerical fields, the number of characters specifies the field width. For
72 example, if ``h`` is the hour, ``h`` might produce "5", but ``hh`` produces
73 "05". For some characters, the count specifies whether an abbreviated or full
74 form should be used […]
75
76 Two single quotes represent a literal single quote, either inside or outside
77 single quotes. Text within single quotes is not interpreted in any way (except
78 for two adjacent single quotes).
79
80 For example:
81
82 .. code-block:: pycon
83
84 >>> d = date(2007, 4, 1)
85 >>> format_date(d, "EEE, MMM d, ''yy", locale='en')
86 u"Sun, Apr 1, '07"
87 >>> format_date(d, "EEEE, d.M.yyyy", locale='de')
88 u'Sonntag, 1.4.2007'
89
90 >>> t = time(15, 30)
91 >>> format_time(t, "hh 'o''clock' a", locale='en')
92 u"03 o'clock PM"
93 >>> format_time(t, 'H:mm a', locale='de')
94 u'15:30 nachm.'
95
96 >>> dt = datetime(2007, 4, 1, 15, 30)
97 >>> format_datetime(dt, "yyyyy.MMMM.dd GGG hh:mm a", locale='en')
98 u'02007.April.01 AD 03:30 PM'
99
100 The syntax for custom datetime format patterns is described in detail in the
101 the `Locale Data Markup Language specification`_. The following table is just a
102 relatively brief overview.
103
104 .. _`Locale Data Markup Language specification`: http://unicode.org/reports/tr35/#Date_Format_Patterns
105
106 Date Fields
107 -----------
108
109 +----------+--------+--------------------------------------------------------+
110 | Field | Symbol | Description |
111 +==========+========+========================================================+
112 | Era | ``G`` | Replaced with the era string for the current date. One |
113 | | | to three letters for the abbreviated form, four |
114 | | | lettersfor the long form, five for the narrow form |
115 +----------+--------+--------------------------------------------------------+
116 | Year | ``y`` | Replaced by the year. Normally the length specifies |
117 | | | the padding, but for two letters it also specifies the |
118 | | | maximum length. |
119 | +--------+--------------------------------------------------------+
120 | | ``Y`` | Same as ``y`` but uses the ISO year-week calendar. |
121 | +--------+--------------------------------------------------------+
122 | | ``u`` | ?? |
123 +----------+--------+--------------------------------------------------------+
124 | Quarter | ``Q`` | Use one or two for the numerical quarter, three for |
125 | | | the abbreviation, or four for the full name. |
126 | +--------+--------------------------------------------------------+
127 | | ``q`` | Use one or two for the numerical quarter, three for |
128 | | | the abbreviation, or four for the full name. |
129 +----------+--------+--------------------------------------------------------+
130 | Month | ``M`` | Use one or two for the numerical month, three for the |
131 | | | abbreviation, or four for the full name, or five for |
132 | | | the narrow name. |
133 | +--------+--------------------------------------------------------+
134 | | ``L`` | Use one or two for the numerical month, three for the |
135 | | | abbreviation, or four for the full name, or 5 for the |
136 | | | narrow name. |
137 +----------+--------+--------------------------------------------------------+
138 | Week | ``w`` | Week of year. |
139 | +--------+--------------------------------------------------------+
140 | | ``W`` | Week of month. |
141 +----------+--------+--------------------------------------------------------+
142 | Day | ``d`` | Day of month. |
143 | +--------+--------------------------------------------------------+
144 | | ``D`` | Day of year. |
145 | +--------+--------------------------------------------------------+
146 | | ``F`` | Day of week in month. |
147 | +--------+--------------------------------------------------------+
148 | | ``g`` | ?? |
149 +----------+--------+--------------------------------------------------------+
150 | Week day | ``E`` | Day of week. Use one through three letters for the |
151 | | | short day, or four for the full name, or five for the |
152 | | | narrow name. |
153 | +--------+--------------------------------------------------------+
154 | | ``e`` | Local day of week. Same as E except adds a numeric |
155 | | | value that will depend on the local starting day of |
156 | | | the week, using one or two letters. |
157 | +--------+--------------------------------------------------------+
158 | | ``c`` | ?? |
159 +----------+--------+--------------------------------------------------------+
160
161 Time Fields
162 -----------
163
164 +----------+--------+--------------------------------------------------------+
165 | Field | Symbol | Description |
166 +==========+========+========================================================+
167 | Period | ``a`` | AM or PM |
168 +----------+--------+--------------------------------------------------------+
169 | Hour | ``h`` | Hour [1-12]. |
170 | +--------+--------------------------------------------------------+
171 | | ``H`` | Hour [0-23]. |
172 | +--------+--------------------------------------------------------+
173 | | ``K`` | Hour [0-11]. |
174 | +--------+--------------------------------------------------------+
175 | | ``k`` | Hour [1-24]. |
176 +----------+--------+--------------------------------------------------------+
177 | Minute | ``m`` | Use one or two for zero places padding. |
178 +----------+--------+--------------------------------------------------------+
179 | Second | ``s`` | Use one or two for zero places padding. |
180 | +--------+--------------------------------------------------------+
181 | | ``S`` | Fractional second, rounds to the count of letters. |
182 | +--------+--------------------------------------------------------+
183 | | ``A`` | Milliseconds in day. |
184 +----------+--------+--------------------------------------------------------+
185 | Timezone | ``z`` | Use one to three letters for the short timezone or |
186 | | | four for the full name. |
187 | +--------+--------------------------------------------------------+
188 | | ``Z`` | Use one to three letters for RFC 822, four letters for |
189 | | | GMT format. |
190 | +--------+--------------------------------------------------------+
191 | | ``v`` | Use one letter for short wall (generic) time, four for |
192 | | | long wall time. |
193 | +--------+--------------------------------------------------------+
194 | | ``V`` | Same as ``z``, except that timezone abbreviations |
195 | | | should be used regardless of whether they are in |
196 | | | common use by the locale. |
197 +----------+--------+--------------------------------------------------------+
198
199
200 Time-zone Support
201 =================
202
203 Many of the verbose time formats include the time-zone, but time-zone
204 information is not by default available for the Python ``datetime`` and
205 ``time`` objects. The standard library includes only the abstract ``tzinfo``
206 class, which you need appropriate implementations for to actually use in your
207 application. Babel includes a ``tzinfo`` implementation for UTC (Universal
208 Time).
209
210 For real time-zone support, it is strongly recommended that you use the
211 third-party package `pytz`_, which includes the definitions of practically all
212 of the time-zones used on the world, as well as important functions for
213 reliably converting from UTC to local time, and vice versa:
214
215 .. code-block:: pycon
216
217 >>> from datetime import time
218 >>> from pytz import timezone, utc
219 >>> dt = datetime(2007, 04, 01, 15, 30, tzinfo=utc)
220 >>> eastern = timezone('US/Eastern')
221 >>> format_datetime(dt, 'H:mm Z', tzinfo=eastern, locale='en_US')
222 u'11:30 -0400'
223
224 The recommended approach to deal with different time-zones in a Python
225 application is to always use UTC internally, and only convert from/to the users
226 time-zone when accepting user input and displaying date/time data, respectively.
227 You can use Babel together with ``pytz`` to apply a time-zone to any
228 ``datetime`` or ``time`` object for display, leaving the original information
229 unchanged:
230
231 .. code-block:: pycon
232
233 >>> british = timezone('Europe/London')
234 >>> format_datetime(dt, 'H:mm zzzz', tzinfo=british, locale='en_US')
235 u'16:30 British Summer Time'
236
237 Here, the given UTC time is adjusted to the "Europe/London" time-zone, and
238 daylight savings time is taken into account. Daylight savings time is also
239 applied to ``format_time``, but because the actual date is unknown in that
240 case, the current day is assumed to determine whether DST or standard time
241 should be used.
242
243 .. _`pytz`: http://pytz.sourceforge.net/
244
245
246 Localized Time-zone Names
247 -------------------------
248
249 While the ``Locale`` class provides access to various locale display names
250 related to time-zones, the process of building a localized name of a time-zone
251 is actually quite complicated. Babel implements it in separately usable
252 functions in the ``babel.dates`` module, most importantly the
253 ``get_timezone_name`` function:
254
255 .. code-block:: pycon
256
257 >>> from pytz import timezone
258 >>> from babel import Locale
259 >>> from babel.dates import get_timezone_name
260
261 >>> tz = timezone('Europe/Berlin')
262 >>> get_timezone_name(tz, locale=Locale.parse('pt_PT'))
263 u'Hor\xe1rio Alemanha'
264
265 You can pass the function either a ``datetime.tzinfo`` object, or a
266 ``datetime.date`` or ``datetime.datetime`` object. If you pass an actual date,
267 the function will be able to take daylight savings time into account. If you
268 pass just the time-zone, Babel does not know whether daylight savings time is
269 in effect, so it uses a generic representation, which is useful for example to
270 display a list of time-zones to the user.
271
272 .. code-block:: pycon
273
274 >>> from datetime import datetime
275
276 >>> dt = tz.localize(datetime(2007, 8, 15))
277 >>> get_timezone_name(dt, locale=Locale.parse('de_DE'))
278 u'Mitteleurop\xe4ische Sommerzeit'
279 >>> get_timezone_name(tz, locale=Locale.parse('de_DE'))
280 u'Deutschland'
281
282
283 Parsing Dates
284 =============
285
286 Babel can also parse date and time information in a locale-sensitive manner:
287
288 .. code-block:: pycon
289
290 >>> from babel.dates import parse_date, parse_datetime, parse_time
291
292 .. note:: Date/time parsing is not properly implemented yet
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