Converting to and from Hindu calendar

Did you check DateTime-Indic-0.1 family of modules? At least DateTime::Indic::Chandramana
seems to have a method to convert traditional date into UTC values (utc_rd_values).

UPDATE:

I suppose Calendar::Saka may be useful as well for many users (as I have known, it’s the Indian national calendar), in particular, to_gregorian() and from_gregorian() methods.

Seems to be a difficult task. According to this discussion at bytes.com there is no clear way to accomplish a 100% correct conversion. But it seems that they are wrong when they assume that the Hindu calendar has only 364 days instead of 365 (or 366 in leap years).

Here you can find a good conversion table including the handling of leap years: http://hinduism.about.com/od/basics/a/monthsdayseras.htm

If it is as easy as written there you can try something like this (php code):

<?php

function convertDateToHinduDate($date) {
    $beginningDayOfMonth = array(
        1 => 21,
        2 => 20,
        3 => 22 + (dateIsLeapYear($date) ? -1 : 0), /* 21 in leap years */
        4 => 21,
        5 => 22,
        6 => 22,
        7 => 23,
        8 => 23,
        9 => 23,
        10 => 23,
        11 => 22,
        12 => 22,
    );

    $daysOfHinduMonth = array(
        1 => 30 + (dateIsLeapYear($date) ? 1 : 0), /* 31 in leap years */
        2 => 31,
        3 => 31,
        4 => 31,
        5 => 31,
        6 => 31,
        7 => 30,
        8 => 30,
        9 => 30,
        10 => 30,
        11 => 30,
        12 => 30,
    );

    $day = (int) date('d', strtotime($date));
    $month = (int) date('m', strtotime($date));
    $year = (int) date('Y', strtotime($date));

    $monthBefore = $day < $beginningDayOfMonth[$month];
    $yearBefore = $month < 3 || ($month == 3 && $day < $beginningDayOfMonth[3]);

    $newYear = $year + 57 + ($yearBefore ? -1 : 0);
    $newMonth = $month - 2 + ($monthBefore ? -1 : 0);
    if($newMonth < 1) $newMonth = 12 + $newMonth;
    $newDay = $day - $beginningDayOfMonth[$month];
    if($newDay < 1) $newDay = $daysOfHinduMonth[$newMonth] + $newDay;

    return date("d-m-Y",  mktime(11, 59, 0, $newMonth, $newDay, $newYear));
}

function dateIsLeapYear($date) {
    return date('L', strtotime($date));
}

$date = date("d-m-Y", strtotime('2012-01-28'));

echo 'Date: ', $date, ' (is leap year: ', dateIsLeapYear($date) ? 'yes' : 'no', ')<br />';
echo 'Converted Hindu date: ', convertDateToHinduDate($date);
?>

Output of this code:

Date: 28-01-2012 (is leap year: yes)
Converted Hindu date: 07-11-2068

But according to the calculator of this Java applet, it should be 05-11-2068 instead of 07-11-2068. So, there are still some conversion rules missing. Maybe you can give me some more information so that i can correct the code above.

For Python, use calendar2 (note: this is not the built-in calendar module).

Sample use:

>>> from calendar2 import *
>>> old_hindu_solar_from_absolute(absolute_from_gregorian(3,1,2012))
(11, 16, 5112)
>>> old_hindu_lunar_from_absolute(absolute_from_gregorian(3,1,2012))
(12, 0, 8, 5112)

I dont know whether it is correct approach or not but
Please go to http://calendarhome.com/converter/ site and download two javascript files astro.js and calendar.js and follow onchange events of Gregorian Date and fetch Indian Civil Date parameters.