python: adding timedeltas, int unsupported operand type

Question

from datetime import datetime, timedelta

frames_load = 0
times_start_dict = [{'timestamp': datetime(2013, 12, 21, 4, 36, 23)}, {'timestamp': datetime(2013, 12, 21, 4, 36, 23)}]
times_end_dict = [{'timestamp': datetime(2013, 12, 21, 4, 36, 53)}, {'timestamp': datetime(2013, 12, 21, 4, 36, 53)}]

for start in times_start_dict:
    for end in times_end_dict:         
        if check_startend(): #dummy function to check other value in dict to see if start/end times match; please comment this out and indent code block to reproduce error
            frames_load += end['timestamp'] - start['timestamp']
            print frames_load
            continue

Output:

Traceback (line 11): "frames_load += end['timestamp'] - start['timestamp']"

TypeError: unsupported operand type(s) for +=: 'int' and 'datetime.timedelta'

Some context:

I'm iterating over two lists consisting of dicts which contain datetime objects for start and end times, respectively. Once a start and end timedelta have been correctly matched (not shown), I find the time elapsed which becomes a timedelta object. I'm assigning it to frames_load so that in the next iteration, I can add the time elapsed (which should always be positive), figuring it's just like incrementing x += 1. However, I'm getting a TypeError which says to me that after the first iteration/calculation, frames_load is now an int and no longer a timedelta object.

How can I add timedeltas to frames_load so that it can display the aggregate/sum timedelta?

Your error message does not match your code block, see the int(...). — user3072164
– user3072164, Commented Dec 30, 2013 at 2:44
@Nabla Thanks for the edit, I'm new to posting/commenting on stack. What do you mean my error does not match the code block? I wrote this to represent my code and error, so perhaps you're pointing to a discrepancy I don't see. Can you elaborate? — Chrispy
– Chrispy, Commented Dec 30, 2013 at 5:36
@nabla do you mean that the error int cannot be added to a timedelta object does not match with line 4? — Chrispy
– Chrispy, Commented Dec 30, 2013 at 5:37
The line you posted in the code is frames_load += end['timestamp'] - start['timestamp']. The same line in the error traceback reads frames_load += int(end['timestamp'] - start['timestamp']). So the code is not the same code that produced the error. This makes it hard to give a precise answer. Also you should show minimal code initializing frames_load and best times_start_dict and times_end_dict as well, so everyone can reproduce the error. — user3072164
– user3072164, Commented Dec 30, 2013 at 6:22
You already have the answer from @alko: instead of frames_load = 0 use frames_load = timedelta(). — Mark Ransom
– Mark Ransom, Commented Dec 30, 2013 at 18:55

alko · Accepted Answer · 2013-12-30 18:51:25Z

2

First, this code could not output 00:00:35, as frames_load=0 initially.

Second, error says it all, you can't add timedelta, i.e. end['timestamp'] - start['timestamp'], to integer, that is to 0.

If you want sum up cumulative timedelta, you should init frames_load=timedelta(). Or following code will do the trick:

times_start_dict = [{'timestamp': datetime(2013, 12, 21, 4, 36, 23)}, 
                    {'timestamp': datetime(2013, 12, 21, 4, 36, 23)}]
times_end_dict = [{'timestamp': datetime(2013, 12, 21, 4, 36, 25)}, 
                  {'timestamp': datetime(2013, 12, 21, 4, 36, 26)}]
print sum((end['timestamp'] - start['timestamp'] 
             for start, end in zip(times_start_dict, times_end_dict)),
          timedelta())

# 0:00:05

answered Dec 30, 2013 at 18:51

alko

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1 Comment

Chrispy Over a year ago

Awesome thank you @alko, nabla, and others who contributed. I had tried a similar approach to initialize frames_load to datetime.timedelta() but that errored. I guess it's the datetime module is implicitly invoked here?

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