no module clear solution for Days Between by Pouf - python coding challenges

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no module solution in Clear category for Days Between by Pouf

def days_diff(date1, date2):
    total = []
    for date in [date1, date2]:
        year = date[0]
        month = date[1]
        a = (14 - month)//12
        y = year - a
        dayN = date[2]+(153*(month + 12*a - 3)+2)//5 + 365*y + y//4 - y//100 + y//400
        total.append(dayN)
    return abs(total[0]-total[1])

Oct. 15, 2014

Comments:

DiZ on Oct. 29, 2015, 4:37 p.m.
Changing the beginning of the year is a nice idea. Maybe extracting a function to compute days would be nicer: <pre class='brush: python'>def days_diff(date1, date2): def days(date): y, m, d = date correction = m <= 2 y -= correction; m += 12*correction - 3 return d + (153*m + 2)//5 + \ 365*y + y//4 - y//100 + y//400 return abs(days(date1) - days(date2)) </pre>

Pouf on Nov. 1, 2015, 9:51 a.m.
Merci ! I always wonder if I should create a function or juste a for loop like I did. How do you decide ?

DiZ on Nov. 1, 2015, 8:13 p.m.
First of all, in this case, there is only two variables to calculate, so using a loop for only two elements doesn't really make sense. Moreover, also in this case, you have already the cost of creating two variables (in terms of memory) and adding the cost of creating a list of these variables to loop on it is certainly useless. Secondly, from a more general point of view, you should try to create a function if code inside the loop is not linked with the loop itself. For example, if you take a search such as BFS or DFS - these algorithms are based on looping on each elements. Here you independantly make a transformation on two variables. For these cases of unitary transformations, I think a function is clearer and more appropriate. Whereas you need to leave a comment to a future reader to explain what your loop does, you can use Python syntax itself to explain your goal, such as: <pre class='brush: python'>new_elements = [parse(old_one) for old_one in old_elements] useful_data = list(map(simple_transformation, old_data)) </pre>

Pouf on Nov. 13, 2015, 8:41 a.m.
Very good points, thank you very much ! I think I understand

veky on Sept. 24, 2017, 7:39 p.m.
If you can't decide, there's always an option in between: a generator function that simply yields the `dayN`, and then you `return abs(next(total)-next(total))`. Worst of both worlds! ;-P :-D

alekseykonotop on Nov. 30, 2018, 1:06 p.m.
Why reinvent the wheel? You can use the library datetime.

Pouf on Nov. 30, 2018, 1:45 p.m.
I was wondering how the module worked and found it interesting

kiplimock on May 17, 2020, 6:36 p.m.
Please include more comments. Following your algorithm could take time. It works though.

krishnaveni09 on June 25, 2020, 1:20 a.m.
@pouf Can you please explain, how this code works? what is a here, how and what is this calculations doing here? [(14-month)//12]. why are using 14 there? And what dayN is here? how that calculation works?

Pouf on June 27, 2020, 6:56 p.m.
Hi krishnaveni09, I am a bit ashamed of this solution, it shouldn't be in Clear category ! This is what I would do today : ```python def daysdiff(date1, date2): return abs(dayssinceorigin(date1) - dayssince_origin(date2)) def dayssinceorigin(date): year, month, days = date <pre class='brush: python'>result = days if month < 3: # before march result += 365 * (year - 1) # full years # number of days from start of previous year to beginning of \`month\` result += (153 * (month + 12 - 3) + 2) // 5 result += leap_days_since_origin(year - 1) else: result += 365 * year # full years # number of days from start of year to beginning of \`month\` result += (153 * (month - 3) + 2) // 5 result += leap_days_since_origin(year) return result </pre> def leapdayssince_origin(year): return year // 4 - year // 100 + year // 400 ``` The `a` variable from before is the `if/else` from this version, disguised with numbers. To understand what it does, you can run this code :) ```python for month in range(1, 13): print(month, (14 - month) // 12) ```

InfinitelyUncertain on Aug. 5, 2020, 12:13 a.m.
This is great. I enjoyed reading this one. But definitely needs some comments to help us along to understanding what's going on.

Pouf on Aug. 5, 2020, 5:14 a.m.
Thank you ! See comment just above yours for a clean version :)

baophuoc1903 on April 28, 2021, 6:03 p.m.
good job!

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