Converts between Gregorian dates and other calendar systems

# convertdate

The convertdate package was originally developed as "Python Date Utils" by Phil Schwartz. It has been significantly updated and expanded.

Available calendars:

• Armenian
• Bahai
• Coptic (Alexandrian)
• French Republican
• Gregorian
• Hebrew
• Indian Civil
• Islamic
• Julian
• Mayan
• Persian
• Positivist
• Mayan
• ISO
• Ordinal (day of year)
• Dublin day count
• Julian day count

The holidays module also provides some useful holiday-calculation, with a focus on North American and Jewish holidays.

## Installing

pip install convertdate

Or download the package and run python setup.py install.

## Examples

>>> from convertdate import french_republican
>>> from convertdate import hebrew
>>> french_republican.from_gregorian(2014, 10, 31)
(223, 2, 9)
>>> hebrew.from_gregorian(2014, 10, 31)
(5775, 8, 7)


Note that in some calendar systems, the day begins at sundown. Convertdate gives the conversion for noon of the day in question.

Each module includes a monthcalendar function, which will generate a calender-like nested list for a year and month (each list of dates runs from Sunday to Saturday)

>>> hebrew.monthcalendar(5775, 8)
[
[None, None, None, None, None, None, 1],
[2, 3, 4, 5, 6, 7, 8],
[9, 10, 11, 12, 13, 14, 15],
[16, 17, 18, 19, 20, 21, 22],
[23, 24, 25, 26, 27, 28, 29]
]

>>> julian.monthcalendar(2015, 1)
[
[None, None, None, 1, 2, 3, 4],
[5, 6, 7, 8, 9, 10, 11],
[12, 13, 14, 15, 16, 17, 18],
[19, 20, 21, 22, 23, 24, 25],
[26, 27, 28, 29, 30, 31, None]
]


## Special Options

### Armenian

The Armenian calendar begins on 11 July 552 (Julian) and has two modes of reckoning. The first is the invariant-length version consisting of 12 months of 30 days each and five epagomenal days; the second is the version established by Yovhannes Sarkawag in 1084, which fixed the first day of the year with respect to the Julian calendar and added a sixth epagomenal day every four years.

By default the invariant calendar is used, but the Sarkawag calendar can be used beginning with the Armenian year 533 (11 August 1084) by passing the parameter method='sarkawag' to the relevant functions.

### French Republican

Leap year calculations in the French Republican calendar are a matter of dispute. By default, convertdate calculates leap years using the autumnal equinox. You can also use one of three more systematic methods proposed over the years.

• Romme, a co-creator of the calendar, proposed leap years in years divisible by four, except for years divisible by 100.
• Some concordances were drawn up in the 19th century that gave leap years every 4 years, in years that give a remainder of three when divided by four (19, 23, 27, etc...).
• Von Mädler proposed leap years in years divisible by four, except for years divisible by 128.

You can specify any of these three methods with the method keyword argument in french_republican conversion functions.

from convertdate import french_republican

# Romme's method
french_republican.to_gregorian(20, 1, 1), method='romme')
# (1811, 9, 23)

# continuous method
french_republican.to_gregorian(20, 1, 1), method='continuous')
# (1811, 9, 24)

# (1811, 9, 23)


All the conversion methods correctly assign the leap years implemented while calendar was in use (3, 7, 11).

## Baha'i

The Bahá'í (Badí) calendar has an intercalary period, Ayyam-i-Há, which occurs between the 18th and 19th months. Dates in this period are returned as month 19, and the month of ‘Alá is reported as month 20.

from convertdate import bahai
# the first day of Ayyam-i-Ha:
bahai.to_gregorian(175, 19, 1)
# (2019, 2, 26)
# The first day of 'Ala:
bahai.to_gregorian(175, 20, 1)
# (2019, 3, 2)


## Before the Common Era

For dates before the Common Era (year 1), convertdate uses astronomical notation: 1 BC is recorded as 0, 2 BC is -1, etc. This makes arithmatic much easier at the expense of ignoring custom.

Note that for dates before 4 CE, convertdate uses the proleptic Julian calendar. The Julian Calendar was in use from 45 BC, but before 4 CE the leap year leap year pattern was irregular.

The proleptic Gregorian calendar is used for dates before 1582 CE, the year of the Gregorian calendar reform.

## Holidays

North American holidays are the current focus of the holidays module, but pull requests are welcome.

from convertdate import holidays

# For simplicity, functions in the holidays module return a tuple
# In the format (year, month, day)

holidays.new_years(2014)
# (2014, 1, 1)

holidays.memorial_day(2014)
# (2014, 5, 26)

# USA is default
holidays.thanksgiving(2014)
# (2014, 11, 27)

# But there is a Canadian option for some holidays
# (2014, 10, 13)

# Mexican national holidays
holidays.natalicio_benito_juarez(2016)
# (2016, 3, 21)

holidays.dia_revolucion(2016)
# (2016, 11, 21)

# Some Jewish holidays are included
holidays.rosh_hashanah(2014)

# Easter can be calculated according to different churches
# ('western', 'orthodox', 'eastern')
# The eastern Christian computation differs from the Orthodox one
# 4 times in each 532-year cycle.

holidays.easter(2019)
# (2019, 4, 21)
holidays.easter(2019, church="orthodox")
# (2019, 4, 28)
holidays.easter(2019, church="orthodox")
# (2019, 4, 28)


## Utils

Convertdate includes some utilities for manipulating and calculating dates.

from convertdate import utils

# Calculate an arbitrary day of the week
THUR = 3
APRIL = 4

# 3rd Thursday in April
utils.nth_day_of_month(3, THUR, APRIL, 2014)
# (2014, 4, 17)

utils.nth_day_of_month(5, THUR, APRIL, 2014)
# IndexError: No 5th day of month 4

# Use 0 for the first argument to get the last weekday of a month
utils.nth_day_of_month(0, THUR, APRIL, 2014)
# (2014, 4, 24)


Note that when calculating weekdays, convertdate uses the convention of the calendar and time modules: Monday is 0, Sunday is 6.

from convertdate import gregorian

SUN = 6

day = gregorian.to_jd(2014, 4, 17)
nextsunday = utils.next_weekday(SUN, day)

gregorian.from_jd(nextsunday)
# (2014, 4, 20)


Other utility functions:

• nearest_weekday
• next_or_current_weekday
• previous_weekday
• previous_or_current_weekday

## Project details

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