[python] How to calculate the time interval between two time strings

I have two times, a start and a stop time, in the format of 10:33:26 (HH:MM:SS). I need the difference between the two times. I've been looking through documentation for Python and searching online and I would imagine it would have something to do with the datetime and/or time modules. I can't get it to work properly and keep finding only how to do this when a date is involved.

Ultimately, I need to calculate the averages of multiple time durations. I got the time differences to work and I'm storing them in a list. I now need to calculate the average. I'm using regular expressions to parse out the original times and then doing the differences.

For the averaging, should I convert to seconds and then average?

This question is related to python time python-2.6

The answer is


Here's a solution that supports finding the difference even if the end time is less than the start time (over midnight interval) such as 23:55:00-00:25:00 (a half an hour duration):

#!/usr/bin/env python
from datetime import datetime, time as datetime_time, timedelta

def time_diff(start, end):
    if isinstance(start, datetime_time): # convert to datetime
        assert isinstance(end, datetime_time)
        start, end = [datetime.combine(datetime.min, t) for t in [start, end]]
    if start <= end: # e.g., 10:33:26-11:15:49
        return end - start
    else: # end < start e.g., 23:55:00-00:25:00
        end += timedelta(1) # +day
        assert end > start
        return end - start

for time_range in ['10:33:26-11:15:49', '23:55:00-00:25:00']:
    s, e = [datetime.strptime(t, '%H:%M:%S') for t in time_range.split('-')]
    print(time_diff(s, e))
    assert time_diff(s, e) == time_diff(s.time(), e.time())

Output

0:42:23
0:30:00

time_diff() returns a timedelta object that you can pass (as a part of the sequence) to a mean() function directly e.g.:

#!/usr/bin/env python
from datetime import timedelta

def mean(data, start=timedelta(0)):
    """Find arithmetic average."""
    return sum(data, start) / len(data)

data = [timedelta(minutes=42, seconds=23), # 0:42:23
        timedelta(minutes=30)] # 0:30:00
print(repr(mean(data)))
# -> datetime.timedelta(0, 2171, 500000) # days, seconds, microseconds

The mean() result is also timedelta() object that you can convert to seconds (td.total_seconds() method (since Python 2.7)), hours (td / timedelta(hours=1) (Python 3)), etc.


Concise if you are just interested in the time elapsed that is under 24 hours. You can format the output as needed in the return statement :

import datetime
def elapsed_interval(start,end):
    elapsed = end - start
    min,secs=divmod(elapsed.days * 86400 + elapsed.seconds, 60)
    hour, minutes = divmod(min, 60)
    return '%.2d:%.2d:%.2d' % (hour,minutes,secs)

if __name__ == '__main__':
    time_start=datetime.datetime.now()
    """ do your process """
    time_end=datetime.datetime.now()
    total_time=elapsed_interval(time_start,time_end)

Structure that represent time difference in Python is called timedelta. If you have start_time and end_time as datetime types you can calculate the difference using - operator like:

diff = end_time - start_time

you should do this before converting to particualr string format (eg. before start_time.strftime(...)). In case you have already string representation you need to convert it back to time/datetime by using strptime method.


Try this -- it's efficient for timing short-term events. If something takes more than an hour, then the final display probably will want some friendly formatting.

import time
start = time.time()

time.sleep(10)  # or do something more productive

done = time.time()
elapsed = done - start
print(elapsed)

The time difference is returned as the number of elapsed seconds.


    import datetime
    
    day = int(input("day[1,2,3,..31]: "))
    month = int(input("Month[1,2,3,...12]: "))
    year = int(input("year[0~2020]: "))
    start_date = datetime.date(year, month, day)
    
    day = int(input("day[1,2,3,..31]: "))
    month = int(input("Month[1,2,3,...12]: "))
    year = int(input("year[0~2020]: "))
    end_date = datetime.date(year, month, day)
    
    time_difference = end_date - start_date
    age = time_difference.days
    print("Total days: " + str(age))

This site says to try:

import datetime as dt
start="09:35:23"
end="10:23:00"
start_dt = dt.datetime.strptime(start, '%H:%M:%S')
end_dt = dt.datetime.strptime(end, '%H:%M:%S')
diff = (end_dt - start_dt) 
diff.seconds/60 

This forum uses time.mktime()


Take a look at the datetime module and the timedelta objects. You should end up constructing a datetime object for the start and stop times, and when you subtract them, you get a timedelta.


import datetime as dt
from dateutil.relativedelta import relativedelta

start = "09:35:23"
end = "10:23:00"
start_dt = dt.datetime.strptime(start, "%H:%M:%S")
end_dt = dt.datetime.strptime(end, "%H:%M:%S")
timedelta_obj = relativedelta(start_dt, end_dt)
print(
    timedelta_obj.years,
    timedelta_obj.months,
    timedelta_obj.days,
    timedelta_obj.hours,
    timedelta_obj.minutes,
    timedelta_obj.seconds,
)

result: 0 0 0 0 -47 -37


I like how this guy does it — https://amalgjose.com/2015/02/19/python-code-for-calculating-the-difference-between-two-time-stamps. Not sure if it has some cons.

But looks neat for me :)

from datetime import datetime
from dateutil.relativedelta import relativedelta

t_a = datetime.now()
t_b = datetime.now()

def diff(t_a, t_b):
    t_diff = relativedelta(t_b, t_a)  # later/end time comes first!
    return '{h}h {m}m {s}s'.format(h=t_diff.hours, m=t_diff.minutes, s=t_diff.seconds)

Regarding to the question you still need to use datetime.strptime() as others said earlier.


Try this

import datetime
import time
start_time = datetime.datetime.now().time().strftime('%H:%M:%S')
time.sleep(5)
end_time = datetime.datetime.now().time().strftime('%H:%M:%S')
total_time=(datetime.datetime.strptime(end_time,'%H:%M:%S') - datetime.datetime.strptime(start_time,'%H:%M:%S'))
print total_time

OUTPUT :

0:00:05

Both time and datetime have a date component.

Normally if you are just dealing with the time part you'd supply a default date. If you are just interested in the difference and know that both times are on the same day then construct a datetime for each with the day set to today and subtract the start from the stop time to get the interval (timedelta).


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