Get difference between two week days that are in string

Sony Khan 0
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Problem Statement: Am developing a custom job scheduler that needs to be run on given days. It takes start date and end date as string and third param is list of week days on which job should run. Start day can be different with given days but first job should run on next valid day Let suppose Start date is 2022-09-07 (so day name is Wednesday) but given frequency days are ["Monday", "Friday", "Saturday"] so i need to run my first job on coming Friday and for this i need to calculate difference between start date and first valid day (in this case it's Friday)

So how can i do this python to run my first job on valid day (that can be in any position of given frequency days list) and also after one job complete i need to also get next valid day. I did some work but unfortunately its not working. Here is what i did

sorted_week_days_list = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday']
start_date = "2022-09-07"

valid_frequency_days = ["Monday", "Tuesday", "Friday"] # It can be any days in sorted order

start_date_object = datetime.datetime.strptime(start_date, "%Y-%m-%d")

given_start_day = start_date_object.strftime("%A")

if given_start_day not in valid_frequency_days:
    # Need help to implement logic to get date for valid day
date datetime python-3.x
1 Answers

You should use the datetime.weekday() method to pull out the day of the week for days of interest. Assuming that you have dates similar to the format you show above, it is easy to convert, and also just use the day index for your "allowable start days" (Monday=0).

Then you can jig up a little function to look for the next start date in your sorted list and figure out how many days you need to wait.

Example below does that and also "rolls over" the weekend as needed.

Code:

from datetime import datetime, timedelta
from bisect import bisect_left

start_date = "2022-09-09"

valid_start_dates = [1, 4] # It can be any days in sorted order

start_date_object = datetime.strptime(start_date, "%Y-%m-%d")

d=start_date_object.weekday()
print(f'the numbered day of the week is: {d}')

def days_till_start(day, valid_start_days):
    idx = bisect_left(valid_start_days, day)
    if idx >= len(valid_start_days): # wrap around to next start
        return valid_start_days[0] + 7 - day
    elif day == valid_start_days[idx]:
        return 0
    else:
        return valid_start_days[idx] - day

print(days_till_start(d, valid_start_dates))

start_dates = ['2022-09-05', '2022-09-06', '2022-09-07', '2022-09-08', '2022-09-09', '2022-09-10']

start_wkdys = [datetime.strptime(d, "%Y-%m-%d").weekday() for d in start_dates]

for d in start_wkdys:
    print(f'day index is: {d}')
    print(f'next start date is {days_till_start(d, valid_start_dates)} away')
    print()

Output:

the numbered day of the week is: 4
0

day index is: 0
next start date is 1 away

day index is: 1
next start date is 0 away

day index is: 2
next start date is 2 away

day index is: 3
next start date is 1 away

day index is: 4
next start date is 0 away

day index is: 5
next start date is 3 away
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