CODEWITHSUNDEEP
pythondatetimezone
daydreamer
daydreamer

Reputation: 92079

How to handle date difference between client and server?

I have an API which looks like

/summary/yyyy/mm

How I calculate remaining days?
This is implemented in python as

def current_financial_month_details(self):
        time_from, time_to = self \
            .get_start_end_time_current_financial_month()

        today = datetime.today()
        from_time = datetime(year=today.year, month=today.month,
                             day=today.day)
        return {
            'time_from': time_from,
            'time_to': time_to,
            'remaining_days': (time_to - from_time).days
        }

The problem?

How do I handle this situation?

Upvotes: 1

Views: 1984

Answers (2)

loopbackbee
loopbackbee

Reputation: 23322

Most people consider best practice to keep storage of dates and times in a timezone independent from geographical location - most commonly UTC. The same applies if you have a service that is going to be accessed (or could eventually be accessed) from locations with different timezones.

As J0HN mentioned, clients should be tasked with converting from/to UTC when they interact with the server. In your case, this means days_left should be defined as the number of days between the current UTC date and the end of the month (in UTC).

For python in particular, there's two types of datetime.datetime objects: naive and timezone-aware. Naive datetimes don't attach any timezone information, so a good practice (in a networked program) is to only use naive datetimes for times in the UTC timezone. To make calculations (subtracting two dates, for instance), consider using datetime.utcnow instead of datetime.now, so you avoid any timezone-associated problems, including (but not limited to) wrong time deltas caused by DST.

If you really need to process other timezones (for displaying to the user, for example), you may need to use a external library, since python, by itself, does not provide a timezone database. This question has more information about that.

Upvotes: 4

Mark Ransom
Mark Ransom

Reputation: 308392

You have a few choices.

First is to specify the time zone that the results are delivered in and expect the clients to live with the discrepancy. Obvious choices are the server timezone or UTC.

Second is to have the API also return the current date as well as the number of days. It won't change the result but at least you'll be able to detect that the date is different than the one you were expecting.

Third is to have the API take a time zone input so that the server can adjust its processing.

Fourth is to make the date change at some time other than midnight, 5 AM for example. This only works if your clients are all in similar timezones and your activity isn't round-the-clock; if you have a client in China you're probably going to regret this option.

Upvotes: 1

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