Given a specific date, find the next date in the list using Python

Question

I have a list of dates. And given a specific input date, want to find the next date in the list. Example is:

my_dates_list = ['2019-01-31', '2019-02-28', '2019-03-31', '2019-04-30', '2019-05-31', '2019-06-30'].
InputDate = '2019-03-31'

the output should be '2019-04-30' because it is the next date of the InputDate found in the list.

Another example: if InputDate is '2019-03-31', the output should be '2019-04-30'.

Maybe sort the list by datetime and take 'Input + 1'? There might be a more pythonic approach out there — Matt Cottrill, Feb 12 '21 at 02:17
"pandas"? your code doesn't use it at all... Anyways you can probably just sort it and binary search — SuperStormer, Feb 12 '21 at 02:17
@SuperStormer What part of the rest of my code would be helpful for this question? — soiledboy, Feb 12 '21 at 02:58

Michael Lee · Accepted Answer · 2021-02-12T03:03:35.920

3

Joe's answer works, but because your dates are zfilled and are ordered year to day, you don't need a parser. Here's a two-line solution.

my_dates_list = ['2019-01-31', '2019-07-13', '2019-02-28', '2019-03-31',
                 '2019-04-30', '2019-05-31', '2019-06-30']
input_date = '2019-03-31'

results = [d for d in sorted(my_dates_list) if d > input_date]
output = results[0] if results else None
print(output)

result = '2019-04-30'

edited Feb 12 '21 at 03:03

answered Feb 12 '21 at 02:58

Michael Lee

698
5
13

1

or using a list comprehension, `result = [d for d in sorted(my_dates_list) if d > input_date][0]` – Mark Reed Feb 12 '21 at 03:03
1

@MarkReed that's much more readable - edited to replace with that. – Michael Lee Feb 12 '21 at 03:05

Joe Ferndz · Answer 2 · 2021-02-12T02:58:29.087

You can convert the string data into datetime using datetime.strptime, then sort them in ascending order, then check if the value is greater than the input value. If you have a value, then you can return it using datetime.strftime. For more details on using datetime, please refer to this Stack Overflow thread Converting Strings into datetime. You can also see additional inputs in this link on Converting between datetime and strings

Here's how I would do it:

from datetime import datetime
my_dates_list = ['2019-01-31', '2019-02-28', '2019-03-31', '2019-04-30', '2019-05-31', '2019-06-30']
my_sorted_dates = [datetime.strptime(i,'%Y-%m-%d') for i in my_dates_list]
my_sorted_dates.sort()

def find_next(x):
    y = [a for a in my_sorted_dates if a > datetime.strptime(x,'%Y-%m-%d')]
    return y[0].strftime('%Y-%m-%d') if y else None

print (find_next('2019-03-12'))

print (find_next('2019-03-31'))

print (find_next('2019-04-30'))

print (find_next('2019-08-30'))

Results will be:

2019-03-31 # for find_next('2019-03-12')

2019-04-30 # for find_next('2019-03-31')

2019-05-31 # for find_next('2019-04-30')

None # for find_next('2019-08-30')

Given a specific date, find the next date in the list using Python

2 Answers2