A simple command line utility implemented in Python for practicing mental calculation of the day of the week for dates in the Gregorian calendar, using the Doomsday rule algorithm originally described by John Horton Conway [1]. This implementation relies on recent improvements to the algorithm by Chamberlain Fong and Michael K. Walters [2] that reduce the complexity of the mental calculation, as well as on the formula for calculating the anchor day for a century described in the Wikipedia entry for the Doomsday rule [3].
$ doomsday --help
Usage: doomsday [OPTIONS] COMMAND [ARGS]...
Options:
--help Show this message and exit.
Commands:
dayofweek Calculate the day of the week for DATE.
doomscentury Calculate the anchor day for the century of YEAR.
doomsmonth Calculate the doomsmonth for DATE.
doomsyear Calculate the doomsyear for YEAR.
leapyear Determine if YEAR is a leap year.
test Estimate your accuracy in calculating the day of the week.
$ doomsday leapyear --help
Usage: doomsday leapyear [OPTIONS] YEAR
Determine if YEAR is a leap year.
Options:
--explain Provide a walkthrough of the calculation.
--help Show this message and exit.
$ doomsday doomscentury --help
Usage: doomsday doomscentury [OPTIONS] YEAR
Calculate the anchor day for the century of YEAR.
Options:
--explain Provide a walkthrough of the calculation.
--help Show this message and exit.
$ doomsday doomsyear --help
Usage: doomsday doomsyear [OPTIONS] YEAR
Calculate the doomsyear for YEAR.
Options:
--explain Provide a walkthrough of the calculation.
--help Show this message and exit.
$ doomsday doomsmonth --help
Usage: doomsday doomsmonth [OPTIONS] [%Y-%m-%d|%Y-%m-%dT%H:%M:%S|%Y-%m-%d
%H:%M:%S]
Calculate the doomsmonth for DATE.
Options:
--explain Provide a walkthrough of the calculation.
--help Show this message and exit.
$ doomsday dayofweek --help
Usage: doomsday dayofweek [OPTIONS] [%Y-%m-%d|%Y-%m-%dT%H:%M:%S|%Y-%m-%d
%H:%M:%S]
Calculate the day of the week for DATE.
Options:
--explain Provide a walkthrough of the calculation.
--help Show this message and exit.
$ doomsday test --help
Usage: doomsday test [OPTIONS]
Estimate your accuracy in calculating the day of the week.
Options:
--trials INTEGER RANGE [1<=x<=100]
--help Show this message and exit.
Python 3.6 or later.
$ pip install doomsday
This code is provided under the terms of an MIT License. See the LICENSE file for the copyright notice.
[1] Berlekamp, E.R., Conway, J.H. and Guy, R. K. Winning Ways for your Mathematical Plays. Volume 2: Games In Particular. Academic Press, NY (1982).
[2] Fong, C. and Walters, M.K. Methods for Accelerating Conway's Doomsday Algorithm (part 2). ICIAM (2011).
[3] Wikipedia. Doomsday rule. Downloaded from http://en.wikipedia.org/wiki/Doomsday_rule (2012).
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