Cannot create a timer with an empty day slot using datetime

Question

I have a program that is supposed to keep a running total of time spent doing something. I have a value stored, that is meant to start at "000d 00h 00m 00s" for 0 days, hours, minutes, and seconds. However, if I try to add a time to it, I receive "ValueError: time data '000d 00h 00m 00s' does not match format '%jd %Hh %Mm %Ss'".

If I change the starting string to '001d 00h 00m 00s' it will add the time no problem, but then I will have a value 24 hours greater than what is accurate. It will also function if I just remove the day counter and have it '00h 00m 00s', but it will then still reset the hours once it hits 24.

Being able to start at '000d 00h 00m 00s' would be preferable, but if that isn't possible, having the hours overflow (i.e. "25h 00m 00s') would work.

from datetime import *

EmptyTime = '000d 00h 00m 00s'
EmptyTimeThatWorks = '001d 00h 00m 00s'
ExampleTime = '174d 19h 07m 53s' # June 23 7:07 PM
FMT = "%jd %Hh %Mm %Ss"

def TaskEnded(RunningTotal, TimerStartTime):
    PresentTime = datetime.now().strftime(FMT) #PresnetTime is when the TaskEnded

    st = datetime.strptime(TimerStartTime, FMT)  #Brings things into the right format 
    pt = datetime.strptime(PresentTime, FMT)  #Brings things into the right format
    rt = datetime.strptime(RunningTotal, FMT)  #Brings things into the right format, but EmptyTime cant be
                                               # conveted to the right time because day '0' doenst exist
                                               # while hour, minute, and second 0 do

    NewTotal = rt + (pt - st)      #takes the running total and adds the timer value, which is the difference of start and end times
    NewTotal2 = datetime.strftime(NewTotal, FMT)  # Puts the Datetime value back into the right format FMT
    print(NewTotal2)
    return NewTotal2

TaskEnded(EmptyTimeThatWorks, ExampleTime)
TaskEnded(EmptyTime, ExampleTime)

Answer 1

Here's what I meant about keeping the elapsed time in a timedelta and writing code that follows the PEP 8 guidelines:

from datetime import *


def task_ended(running_total, timer_start_time, fmt="%B %d, %Y %I:%M %p"):
    """ Add time elapsed between timer_start_time and now to
        running_total timedelta and return it.
    """
    present_time = datetime.now()   # When task ended.
    # Convert timer_start_time string into a datetime using fmt string.
    start_time = datetime.strptime(timer_start_time, fmt)
    # Add time elapsed between present time and timer start time to running
    # total and return it.
    return running_total + (present_time - start_time)

def format_timedelta(td):
    """ Format timedelta into custom string representation. """
    days = td.days
    hours, remainder = divmod(td.seconds, 3600)
    mins, secs = divmod(remainder, 60)
    return '{:03}d {:02}h {:02}m {:02}s'.format(days, hours, mins, secs)


running_total = timedelta()
example_start_time = 'June 25, 2019 5:00 PM'
running_total = task_ended(running_total, example_start_time)
print('running total:', format_timedelta(running_total))
print()
running_total = timedelta()
example_start_time = 'June 23, 2019 7:07 PM'
running_total = task_ended(running_total, example_start_time)
print('running total:', format_timedelta(running_total))

Here's a way to parse a running total string into a timedelta (based on a couple of the answers to the question How to construct a timedelta object from a simple string):

import re

regex = re.compile(r'^((?P<days>[\d]+?)d)? *'
                   r'((?P<hours>[\d]+?)h)? *'
                   r'((?P<minutes>[\d]+?)m)? *'
                   r'((?P<seconds>[\d]+?)s)?$')

def parse_timedelta(time_str):
    """
    Parse a time string e.g. (2h 13m) into a timedelta object.

    Modified from virhilo & Peter's answers at https://stackoverflow.com/a/4628148/355230

    :param time_str: A string identifying a duration.  (eg. 2h 13m)
    :return datetime.timedelta: A datetime.timedelta object
    """
    parts = regex.match(time_str)
    assert parts is not None, "Could not parse any time information from '{}'".format(time_str)
    time_params = {name: float(param) for name, param in parts.groupdict().items() if param}
    return timedelta(**time_params)


# Test string parser function.
test_str = '000d 21h 40m 53s'
td = parse_timedelta(test_str)
assert format_timedelta(td) == test_str

test_str = '002d 19h 33m 53s'
td = parse_timedelta(test_str)
assert format_timedelta(td) == test_str