native_days_between clear solution for Days Between by Jon_Red - python coding challenges

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native_days_between solution in Clear category for Days Between by Jon_Red

def days_diff(a,b):
    t=[]
    for d in[a,b]:
        m,y=(14-d[1])//12,d[0]-(14-d[1])//12
        t.append(d[2]+(153*(d[1]+12*m-3)+2)//5+365*y+y//4-y//100+y//400)
    return abs(t[0]-t[1])


if __name__=='__main__':
    # self-checks
    assert days_diff((1982,4,19),(1982,4,22))==3
    assert days_diff((2014,1,1),(2014,8,27))==238
    assert days_diff((2014,8,27),(2014,1,1))==238

July 22, 2020

Comments:

Elena_Korljukova on July 23, 2020, 9:56 a.m.
Cool! Did you derive the formulas yourself?

Jon_Red on July 23, 2020, 2:03 p.m.
Nah, I borrowed this particular formula from <a href="https://py.checkio.org/mission/days-diff/publications/Pouf/python-3/no-module/">this solution</a>. It's an abbreviated ordinal breakdown which I've found great for simple stuff like counting days or determining day of week. Deriving an exact date from an ordinal with no module, on the other hand, is a much more complicated affair. I found this out when writing a solution for <a href="https://py.checkio.org/mission/the-first-working-day/publications/Jon_Red/python-3/native_the_first_working_day/">thefirstworking_day</a>. I had to work those formulas out by looking through the actual datetime module itself.

Striga on Sept. 28, 2020, 7:36 p.m.
Creative!

Stensen on Sept. 29, 2020, 3:14 p.m.
I am trying to understand :P

Stensen on Sept. 29, 2020, 3:15 p.m.
Weel, I won't say I enjoyed reading it but Nice solution so far :D

Jon_Red on Oct. 3, 2020, 6:54 p.m.
We convert the dates into ordinals which we then store in the t array. Ordinals are essentially the number of days since 1-1-0001. Then we return the difference of t[0] and t[1]. The <a href="https://github.com/python/cpython/blob/master/Lib/datetime.py">datetime</a> module (which is based off of <a href="https://github.com/naftaliharris/tauthon/blob/master/Demo/classes/Dates.py">dates.py</a>) operate off this same basic logic.

Stensen on Oct. 3, 2020, 8:40 p.m.
Ooh Thanks for these valuable information! I really enjoyed reading that dates.py script :)

Master of the Time Stone

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