Django date template helpers without relying on Django

date_helper.py

# Django licence
"""
Copyright (c) Django Software Foundation and individual contributors.
All rights reserved.

Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright notice, 
       this list of conditions and the following disclaimer.
    
    2. Redistributions in binary form must reproduce the above copyright 
       notice, this list of conditions and the following disclaimer in the
       documentation and/or other materials provided with the distribution.

    3. Neither the name of Django nor the names of its contributors may be used
       to endorse or promote products derived from this software without
       specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
"""

import re
import time
import calendar
import pytz

def _(x):
    "Pretends to be gettext"
    return x

# Django's associated press hard coded day names
WEEKDAYS = {
    0:_('Monday'), 1:_('Tuesday'), 2:_('Wednesday'), 3:_('Thursday'), 4:_('Friday'),
    5:_('Saturday'), 6:_('Sunday')
}
WEEKDAYS_ABBR = {
    0:_('Mon'), 1:_('Tue'), 2:_('Wed'), 3:_('Thu'), 4:_('Fri'),
    5:_('Sat'), 6:_('Sun')
}
WEEKDAYS_REV = {
    'monday':0, 'tuesday':1, 'wednesday':2, 'thursday':3, 'friday':4,
    'saturday':5, 'sunday':6
}
MONTHS = {
    1:_('January'), 2:_('February'), 3:_('March'), 4:_('April'), 5:_('May'), 6:_('June'),
    7:_('July'), 8:_('August'), 9:_('September'), 10:_('October'), 11:_('November'),
    12:_('December')
}
MONTHS_3 = {
    1:_('jan'), 2:_('feb'), 3:_('mar'), 4:_('apr'), 5:_('may'), 6:_('jun'),
    7:_('jul'), 8:_('aug'), 9:_('sep'), 10:_('oct'), 11:_('nov'), 12:_('dec')
}
MONTHS_3_REV = {
    'jan':1, 'feb':2, 'mar':3, 'apr':4, 'may':5, 'jun':6, 'jul':7, 'aug':8,
    'sep':9, 'oct':10, 'nov':11, 'dec':12
}
MONTHS_AP = { # month names in Associated Press style
    1:_('Jan.'), 2:_('Feb.'), 3:_('March'), 4:_('April'), 5:_('May'), 6:_('June'), 7:_('July'),
    8:_('Aug.'), 9:_('Sept.'), 10:_('Oct.'), 11:_('Nov.'), 12:_('Dec.')
}

re_formatchars = re.compile(r'(?<!\\)([aAbBdDfFgGhHiIjlLmMnNOPrsStTUwWyYzZ])')
re_escaped = re.compile(r'\\(.)')

class Formatter(object):
    def format(self, formatstr):
        pieces = []
        for i, piece in enumerate(re_formatchars.split(unicode(formatstr))):
            if i % 2:
                pieces.append(unicode(getattr(self, piece)()))
            elif piece:
                pieces.append(re_escaped.sub(r'\1', piece))
        return u''.join(pieces)


class TimeFormat(Formatter):
    def __init__(self, t):
        self.data = t

    def a(self):
        "'a.m.' or 'p.m.'"
        if self.data.hour > 11:
            return _('p.m.')
        return _('a.m.')

    def A(self):
        "'AM' or 'PM'"
        if self.data.hour > 11:
            return _('PM')
        return _('AM')

    def B(self):
        "Swatch Internet time"
        raise NotImplementedError

    def f(self):
        """
        Time, in 12-hour hours and minutes, with minutes left off if they're
        zero.
        Examples: '1', '1:30', '2:05', '2'
        Proprietary extension.
        """
        if self.data.minute == 0:
            return self.g()
        return u'%s:%s' % (self.g(), self.i())

    def g(self):
        "Hour, 12-hour format without leading zeros; i.e. '1' to '12'"
        if self.data.hour == 0:
            return 12
        if self.data.hour > 12:
            return self.data.hour - 12
        return self.data.hour

    def G(self):
        "Hour, 24-hour format without leading zeros; i.e. '0' to '23'"
        return self.data.hour

    def h(self):
        "Hour, 12-hour format; i.e. '01' to '12'"
        return u'%02d' % self.g()

    def H(self):
        "Hour, 24-hour format; i.e. '00' to '23'"
        return u'%02d' % self.G()

    def i(self):
        "Minutes; i.e. '00' to '59'"
        return u'%02d' % self.data.minute

    def P(self):
        """
        Time, in 12-hour hours, minutes and 'a.m.'/'p.m.', with minutes left off
        if they're zero and the strings 'midnight' and 'noon' if appropriate.
        Examples: '1 a.m.', '1:30 p.m.', 'midnight', 'noon', '12:30 p.m.'
        Proprietary extension.
        """
        if self.data.minute == 0 and self.data.hour == 0:
            return _('midnight')
        if self.data.minute == 0 and self.data.hour == 12:
            return _('noon')
        return u'%s %s' % (self.f(), self.a())

    def s(self):
        "Seconds; i.e. '00' to '59'"
        return u'%02d' % self.data.second


class DateFormat(TimeFormat):
    year_days = [None, 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334]

    def __init__(self, dt):
        # Accepts either a datetime or date object.
        self.data = dt
        self.timezone = getattr(dt, 'tzinfo', None)
        if hasattr(self.data, 'hour') and not self.timezone:
            self.timezone = pytz.timezone('Europe/London')

    def b(self):
        "Month, textual, 3 letters, lowercase; e.g. 'jan'"
        return MONTHS_3[self.data.month]

    def d(self):
        "Day of the month, 2 digits with leading zeros; i.e. '01' to '31'"
        return u'%02d' % self.data.day

    def D(self):
        "Day of the week, textual, 3 letters; e.g. 'Fri'"
        return WEEKDAYS_ABBR[self.data.weekday()]

    def F(self):
        "Month, textual, long; e.g. 'January'"
        return MONTHS[self.data.month]

    def I(self):
        "'1' if Daylight Savings Time, '0' otherwise."
        if self.timezone and self.timezone.dst(self.data):
            return u'1'
        else:
            return u'0'

    def j(self):
        "Day of the month without leading zeros; i.e. '1' to '31'"
        return self.data.day

    def l(self):
        "Day of the week, textual, long; e.g. 'Friday'"
        return WEEKDAYS[self.data.weekday()]

    def L(self):
        "Boolean for whether it is a leap year; i.e. True or False"
        return calendar.isleap(self.data.year)

    def m(self):
        "Month; i.e. '01' to '12'"
        return u'%02d' % self.data.month

    def M(self):
        "Month, textual, 3 letters; e.g. 'Jan'"
        return MONTHS_3[self.data.month].title()

    def n(self):
        "Month without leading zeros; i.e. '1' to '12'"
        return self.data.month

    def N(self):
        "Month abbreviation in Associated Press style. Proprietary extension."
        return MONTHS_AP[self.data.month]

    def O(self):
        "Difference to Greenwich time in hours; e.g. '+0200'"
        seconds = self.Z()
        return u"%+03d%02d" % (seconds // 3600, (seconds // 60) % 60)

    def r(self):
        "RFC 2822 formatted date; e.g. 'Thu, 21 Dec 2000 16:01:07 +0200'"
        return self.format('D, j M Y H:i:s O')

    def S(self):
        "English ordinal suffix for the day of the month, 2 characters; i.e. 'st', 'nd', 'rd' or 'th'"
        if self.data.day in (11, 12, 13): # Special case
            return u'th'
        last = self.data.day % 10
        if last == 1:
            return u'st'
        if last == 2:
            return u'nd'
        if last == 3:
            return u'rd'
        return u'th'

    def t(self):
        "Number of days in the given month; i.e. '28' to '31'"
        return u'%02d' % calendar.monthrange(self.data.year, self.data.month)[1]

    def T(self):
        "Time zone of this machine; e.g. 'EST' or 'MDT'"
        name = self.timezone and self.timezone.tzname(self.data) or None
        if name is None:
            name = self.format('O')
        return unicode(name)

    def U(self):
        "Seconds since the Unix epoch (January 1 1970 00:00:00 GMT)"
        if getattr(self.data, 'tzinfo', None):
            return int(calendar.timegm(self.data.utctimetuple()))
        else:
            return int(time.mktime(self.data.timetuple()))

    def w(self):
        "Day of the week, numeric, i.e. '0' (Sunday) to '6' (Saturday)"
        return (self.data.weekday() + 1) % 7

    def W(self):
        "ISO-8601 week number of year, weeks starting on Monday"
        # Algorithm from http://www.personal.ecu.edu/mccartyr/ISOwdALG.txt
        week_number = None
        jan1_weekday = self.data.replace(month=1, day=1).weekday() + 1
        weekday = self.data.weekday() + 1
        day_of_year = self.z()
        if day_of_year <= (8 - jan1_weekday) and jan1_weekday > 4:
            if jan1_weekday == 5 or (jan1_weekday == 6 and calendar.isleap(self.data.year-1)):
                week_number = 53
            else:
                week_number = 52
        else:
            if calendar.isleap(self.data.year):
                i = 366
            else:
                i = 365
            if (i - day_of_year) < (4 - weekday):
                week_number = 1
            else:
                j = day_of_year + (7 - weekday) + (jan1_weekday - 1)
                week_number = j // 7
                if jan1_weekday > 4:
                    week_number -= 1
        return week_number

    def y(self):
        "Year, 2 digits; e.g. '99'"
        return unicode(self.data.year)[2:]

    def Y(self):
        "Year, 4 digits; e.g. '1999'"
        return self.data.year

    def z(self):
        "Day of the year; i.e. '0' to '365'"
        doy = self.year_days[self.data.month] + self.data.day
        if self.L() and self.data.month > 2:
            doy += 1
        return doy

    def Z(self):
        """
        Time zone offset in seconds (i.e. '-43200' to '43200'). The offset for
        timezones west of UTC is always negative, and for those east of UTC is
        always positive.
        """
        if not self.timezone:
            return 0
        offset = self.timezone.utcoffset(self.data)
        # Only days can be negative, so negative offsets have days=-1 and
        # seconds positive. Positive offsets have days=0
        return offset.days * 86400 + offset.seconds


def format(value, format_string):
    "Convenience function"
    df = DateFormat(value)
    return df.format(format_string)

def time_format(value, format_string):
    "Convenience function"
    tf = TimeFormat(value)
    return tf.format(format_string)

# Template helpers


def date(value, arg=None):
    """Formats a date according to the given format."""
    if not value:
        return u''
    if arg is None:
        raise TypeError("Invalid argument")
    try:
        return format(value, arg)
    except AttributeError:
        return ''

def time(value, arg=None):
    """Formats a time according to the given format."""
    if value in (None, u''):
        return u''
    if arg is None:
        raise TypeError("Invalid argument")
    try:
        return time_format(value, arg)
    except AttributeError:
        return ''