Add support for date-time skeletons

The skeletons for dates and times are described on
http://cldr.unicode.org/translation/date-time-patterns under
Additional Date-Time Formats. And are useful when you want to some more
control over formatting dates and times but don't want to force all
locales to use the same pattern.

babel/core.py

@@ -731,6 +731,19 @@ def datetime_formats(self):
         """
         return self._data['datetime_formats']
 
+    @property
+    def datetime_skeletons(self):
+        """Locale patterns for formatting parts of a datetime.
+
+        >>> Locale('en').datetime_skeletons['MEd']
+        <DateTimePattern u'E, M/d'>
+        >>> Locale('fr').datetime_skeletons['MEd']
+        <DateTimePattern u'E dd/MM'>
+        >>> Locale('fr').datetime_skeletons['H']
+        <DateTimePattern u"HH 'h'">
+        """
+        return self._data['datetime_skeletons']
+
     @property
     def plural_form(self):
         """Plural rules for the locale.

babel/dates.py

@@ -694,6 +694,34 @@ def format_time(time=None, format='medium', tzinfo=None, locale=LC_TIME):
     return parse_pattern(format).apply(time, locale)
 
 
+def format_skeleton(skeleton, datetime=None, tzinfo=None, locale=LC_TIME):
+    r"""Return a time and/or date formatted according to the given pattern.
+
+    The skeletons are defined in the CLDR data and provide more flexibility
+    than the simple short/long/medium formats, but are a bit harder to use.
+    The are defined using the date/time symbols without order or punctuation
+    and map to a suitable format for the given locale.
+
+    >>> t = datetime(2007, 4, 1, 15, 30)
+    >>> format_skeleton('MMMEd', t, locale='fr')
+    u'dim. 1 avr.'
+    >>> format_skeleton('MMMEd', t, locale='en')
+    u'Sun, Apr 1'
+
+    After the skeleton is resolved to a pattern `format_datetime` is called so
+    all timezone processing etc is the same as for that.
+
+    :param skeleton: A date time skeleton as defined in the cldr data.
+    :param datetime: the ``time`` or ``datetime`` object; if `None`, the current
+                 time in UTC is used
+    :param tzinfo: the time-zone to apply to the time for display
+    :param locale: a `Locale` object or a locale identifier
+    """
+    locale = Locale.parse(locale)
+    format = locale.datetime_skeletons[skeleton]
+    return format_datetime(datetime, format, tzinfo, locale)
+
+
 TIMEDELTA_UNITS = (
     ('year',   3600 * 24 * 365),
     ('month',  3600 * 24 * 30),

scripts/import_cldr.py

@@ -576,6 +576,7 @@ def main():
                         )
 
             datetime_formats = data.setdefault('datetime_formats', {})
+            datetime_skeletons = data.setdefault('datetime_skeletons', {})
             for format in calendar.findall('dateTimeFormats'):
                 for elem in format.getiterator():
                     if elem.tag == 'dateTimeFormatLength':
@@ -591,6 +592,10 @@ def main():
                         datetime_formats = Alias(_translate_alias(
                             ['datetime_formats'], elem.attrib['path'])
                         )
+                    elif elem.tag == 'availableFormats':
+                        for datetime_skeleton in elem.findall('dateFormatItem'):
+                            datetime_skeletons[datetime_skeleton.attrib['id']] = \
+                                dates.parse_pattern(text_type(datetime_skeleton.text))
 
         # <numbers>
 

tests/test_core.py

@@ -236,6 +236,10 @@ def test_datetime_formats_property(self):
         assert Locale('en').datetime_formats['full'] == u"{1} 'at' {0}"
         assert Locale('th').datetime_formats['medium'] == u'{1} {0}'
 
+    def test_datetime_skeleton_property(self):
+        assert Locale('en').datetime_skeletons['Md'].pattern == u"M/d"
+        assert Locale('th').datetime_skeletons['Md'].pattern == u'd/M'
+
     def test_plural_form_property(self):
         assert Locale('en').plural_form(1) == 'one'
         assert Locale('en').plural_form(0) == 'other'

tests/test_dates.py

@@ -498,6 +498,15 @@ def test_format_time():
     assert us_east == u'3:30:00 PM Eastern Standard Time'
 
 
+def test_format_skeleton():
+    dt = datetime(2007, 4, 1, 15, 30)
+    assert (dates.format_skeleton('yMEd', dt, locale='en_US') == u'Sun, 4/1/2007')
+    assert (dates.format_skeleton('yMEd', dt, locale='th') == u'อา. 1/4/2007')
+
+    assert (dates.format_skeleton('EHm', dt, locale='en') == u'Sun 15:30')
+    assert (dates.format_skeleton('EHm', dt, tzinfo=timezone('Asia/Bangkok'), locale='th') == u'อา. 22:30 น.')
+
+
 def test_format_timedelta():
     assert (dates.format_timedelta(timedelta(weeks=12), locale='en_US')
             == u'3 months')