django/utils/datetime_safe.py

# Python's datetime strftime doesn't handle dates before 1900.
# These classes override date and datetime to support the formatting of a date
# through its full "proleptic Gregorian" date range.
#
# Based on code submitted to comp.lang.python by Andrew Dalke
#
# >>> datetime_safe.date(1850, 8, 2).strftime("%Y/%m/%d was a %A")
# '1850/08/02 was a Friday'

import re
import time as ttime
from datetime import (
    date as real_date, datetime as real_datetime, time as real_time,
)


class date(real_date):
    def strftime(self, fmt):
        return strftime(self, fmt)


class datetime(real_datetime):
    def strftime(self, fmt):
        return strftime(self, fmt)

    @classmethod
    def combine(cls, date, time):
        return cls(date.year, date.month, date.day,
                   time.hour, time.minute, time.second,
                   time.microsecond, time.tzinfo)

    def date(self):
        return date(self.year, self.month, self.day)


class time(real_time):
    pass


def new_date(d):
    "Generate a safe date from a datetime.date object."
    return date(d.year, d.month, d.day)


def new_datetime(d):
    """
    Generate a safe datetime from a datetime.date or datetime.datetime object.
    """
    kw = [d.year, d.month, d.day]
    if isinstance(d, real_datetime):
        kw.extend([d.hour, d.minute, d.second, d.microsecond, d.tzinfo])
    return datetime(*kw)


# This library does not support strftime's "%s" or "%y" format strings.
# Allowed if there's an even number of "%"s because they are escaped.
_illegal_formatting = re.compile(r"((^|[^%])(%%)*%[sy])")


def _findall(text, substr):
    # Also finds overlaps
    sites = []
    i = 0
    while 1:
        j = text.find(substr, i)
        if j == -1:
            break
        sites.append(j)
        i = j + 1
    return sites


def strftime(dt, fmt):
    if dt.year >= 1900:
        return super(type(dt), dt).strftime(fmt)
    illegal_formatting = _illegal_formatting.search(fmt)
    if illegal_formatting:
        raise TypeError("strftime of dates before 1900 does not handle" + illegal_formatting.group(0))

    year = dt.year
    # For every non-leap year century, advance by
    # 6 years to get into the 28-year repeat cycle
    delta = 2000 - year
    off = 6 * (delta // 100 + delta // 400)
    year = year + off

    # Move to around the year 2000
    year = year + ((2000 - year) // 28) * 28
    timetuple = dt.timetuple()
    s1 = ttime.strftime(fmt, (year,) + timetuple[1:])
    sites1 = _findall(s1, str(year))

    s2 = ttime.strftime(fmt, (year + 28,) + timetuple[1:])
    sites2 = _findall(s2, str(year + 28))

    sites = []
    for site in sites1:
        if site in sites2:
            sites.append(site)

    s = s1
    syear = "%04d" % (dt.year,)
    for site in sites:
        s = s[:site] + syear + s[site + 4:]
    return s