Calendrical calculations allowing date conversion between the Gregorian, Revised Julian (Milanković), and Julian calendars.
These functions use the concept of a Chronological Julian Day Number (CJDN). Using these functions, a date on any of the Gregorian, Revised Julian (Milanković), or Julian calendars may be converted to a date on one of the other of those calendars.
The Chronological Julian Day Number is a whole number representing a day. Its day begins at 00:00 Local Time. The zero point for a Julian Date (JD 0.0) corresponds to 12.00 UTC, 1 January -4712 (i.e. 4713 BC). The zero point for the CJDN is 1 January -4712 (the whole day in local time). For more information see: Julian Day .
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Conversions from a calendar date to a CJDN
pGregorianToCJDN: expects Year, Month, Day as strings or integers. Outputs a Chronological Julian Day Number (CJDN) for the given date on the Gregorian calendar.pMilankovicToCJDN: expects Year, Month, Day as strings or integers. Outputs a Chronological Julian Day Number (CJDN) for the given date on the Revised Julian (or Milanković) calendar.pJulianToCJDN: expects Year, Month, Day as strings or integers. Outputs a Chronological Julian Day Number (CJDN) for the given date on the Julian calendar.
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Conversions from CJDN to calendar dates
pCJDNToGregorian: Expects a CJDN. There are also three optional parameters, which all default to False. This function usually returns a date on the Gregorian calendar for a given CJDN. The date is a string in ISO 8601 YYYY-MM-DD format. If, however, one of the optional parameters is set to True (in order: Year, Month, Day), that part of the date (i.e. the year, the month, or the day) is returned as an integer.pCJDNToMilankovic: Expects a CJDN. There are also three optional parameters, which all default to False. This function usually returns a date on the Revised Julian (or Milanković) calendar for a given CJDN. The date is a string in ISO 8601 YYYY-MM-DD format. If, however, one of the optional parameters is set to True (in order: Year, Month, Day), that part of the date (i.e. the year, the month, or the day) is returned as an integer.pCJDNToJulian: Expects a CJDN. There are also three optional parameters, which all default to False. This function usually returns a date on the Julian calendar for a given CJDN. The date is a string in ISO 8601 YYYY-MM-DD format. If, however, one of the optional parameters is set to True (in order: Year, Month, Day), that part of the date (i.e. the year, the month, or the day) is returned as an integer.
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DoW: expects a CJDN. It returns the day of the week for the given CJDN. The day of the week is returned as an ISO 8601 integer, where Monday = 1 and Sunday = 7.
This Python script imports datetime and two functions (floor and fmod) from the math package. The script is written in Python 3 (minimum version 0x030000F0). As most of it consists of mathematical calculations, I do not envisage any issues using the functions in an earlier version of Python.