Days between dates

From Rosetta Code
Revision as of 11:37, 30 September 2019 by rosettacode>Poetaster (some inline explanations)
Task
Days between dates
You are encouraged to solve this task according to the task description, using any language you may know.
Task

Calculate the number of days between two dates. Date input should be in the form YYYY-MM-DD.

The initial example in python is derived from discussion at: https://stackoverflow.com/questions/12862226/the-implementation-of-calculating-the-number-of-days-between-2-dates

This example is similar to one described on the following page as the origin based algorithm, there implemented in c: http://www.sunshine2k.de/articles/coding/datediffindays/calcdiffofdatesindates.html.


Python

<lang python>

  1. !/usr/bin/python

import sys

Difference between two dates = g(y2,m2,d2) - g(y1,m1,d1)

   Where g() gives us the Gregorian Calendar Day

def days( y,m,d ):

  input year and month are shifted to begin the year in march
 m = (m + 9) % 12 
 y = y - m/10
  with (m*306 + 5)/10 the number of days from march 1 to the current 'm' month 
 result = 365*y + y/4 - y/100 + y/400 + (m*306 + 5)/10 + ( d - 1 )
 return result

def diff(one,two):

 [y1,m1,d1] = one.split('-')
 [y2,m2,d2] = two.split('-')
 # strings to integers
 year2 = days( int(y2),int(m2),int(d2))
 year1 = days( int(y1), int(m1), int(d1) )
 return year2 - year1

if __name__ == "__main__":

 one = sys.argv[1]
 two = sys.argv[2]
 print diff(one,two)

</lang>

Output:
python days-between.py 2019-01-01 2019-09-30
272