python - Find the closest date from today in a list

Question

My objective is to get the next closest date (in the future, not past) to today's date from a list. For simplicity's sake, the list (in the format of e.g. 2017-01-31; YYYY-MM-DD) is each football game in the season and I am trying to create a script that in part finds the "next" football game.

I have searched the internet and Stack Overflow for answers and found a promising post, however the solutions provided are using a different format and when I try to tailor it to mine, it trips exceptions.

My logic includes parsing an RSS feed, so I am just going to provide the raw list instead. With this in mind, my simplified code is as follows:

today = str(datetime.date.today())
print(today)

scheduledatelist = ['2017-09-01', '2017-09-09', '2017-09-16', '2017-09-23', '2017-09-30', '2017-10-07', '2017-10-14', '2017-10-21', '2017-10-27', '2017-11-11', '2017-11-18', '2017-11-25']
scheduledatelist = list(reversed(scheduledatelist)) #purpose: to have earliest dates first

This is my attempt at adapting the previous post's solution (I am not well versed in functional programming, so I may not be adapting it right):

get_datetime = lambda s: datetime.datetime.strptime(s, "%Y-%m-%d")
base = get_datetime(today)
later = filter(lambda d: today(d[0]) > today, scheduledatelist)
closest_date = min(later, key = lambda d: today(d[0]))
print(closest_date)

Regardless of my attempt (which may not be the best in my situation as it changes the format and I need the end value to still be YYYY-MM-DD), is there an easier way of doing this? I need that next game (closest to today) value as that will continue on to be used in my logic. So to recap, how can I find the closest date in my list, looking toward the future, from today. Thank you for your help!

Answer 1

first of all let's create datetime.date objects from strings using datetime.datetime.strptime and datetime.datetime.date methods since datetime.date objects are ordered and easier to work with:

date_format = '%Y-%m-%d'
dates = [datetime.datetime.strptime(date_string,
                                    date_format).date()

then let's filter out dates that take place in future (after today)

today = datetime.date.today()
future_dates = [date
                for date in dates
                if date >= today]

then we can simply find next closest date using min

next_closest_date = min(future_dates)

which gives us

>>>next_closest_date
2017-09-01

for given example

---

WARNING

If there is no dates going after today this will cause error like

ValueError: min() arg is an empty sequence

if it's ok then we can leave it, but if we don't want to get errors – we can specify default value for min in case of empty sequence like

next_closest_date = min(future_dates, default=None)

---

Finally we can write a function as follows

import datetime


# `default` value is returned when there is no future date strings found
def get_next_closest_date(date_strings, date_format, default=None):
    today = datetime.date.today()
    dates = [datetime.datetime.strptime(date_string,
                                        date_format).date()
             for date_string in date_strings]
    future_dates = [date
                    for date in dates
                    if date >= today]
    return min(future_dates, default)

and use it like

scheduledatelist = ['2017-09-01', '2017-09-09', '2017-09-16', '2017-09-23',
                    '2017-09-30', '2017-10-07', '2017-10-14', '2017-10-21',
                    '2017-10-27', '2017-11-11', '2017-11-18', '2017-11-25']
next_closest_date = get_next_closest_date(date_strings=scheduledatelist,
                                          date_format='%Y-%m-%d')
print(next_closest_date)