问题
I have created a list of timedelta objects and i need to get the average of this list. when i try to do
return (sum(delta_list)/(len(delta_list)-1))
i get TypeError: unsupported operand type(s) for +: 'int' and 'datetime.timedelta'
i am new at working with pythons datetime classes. I also would like to know how to get this average into a format like days: hours: mins: i don't need anything smaller than mins.
回答1:
sum wants a starting value, which is 0 by default, but 0 can't be added to a timedelta so you get the error.
You just have to give sum a timedelta() as the start value:
# this is the average
return sum(delta_list, timedelta()) / len(delta_list)
To print it out you can do this:
print str(some_delta)
If you want something customized you can get some_delta.days and some_delta.seconds but you have to calculate everything between.
回答2:
First of all, sum adds all of the elements from the list to an initial value, which is by default 0 (an integer with value of zero). So to be able to use sum on a list of timedelta's, you need to pass a timedelta(0) argument - sum(delta_list, timedelta(0)).
Secondly, why do you want to subtract one from the length of the list? If a list is of length 1 you'll get a ZeroDivisionError.
Having fixed the above you'll end up with a timedelta object being an average. How to convert that to a human-readable format I'm leaving for you as an exercise. The datetime module documentation should answer all of the possible questions.
回答3:
The sum() function needs a start value to add all the items in the iterable to. It defaults to 0 which is why you're getting the error about adding a timedelta to an int.
To fix this, just pass a timedelta object as the second argument to sum:
(Creating a timedelta with no arguments creates one corresponding to a zero time difference.)
Also, the mean of a set of items is usually the sum of items divided by the number of items so you don't need to subtract 1 from len(delta_list).
These changes mean we can remove some of the brackets from your statement.
So this gives you:
return sum(delta_list,timedelta()) / len(delta_list)
回答4:
A datetime.timedelta object has attributes to access the days, microseconds, and seconds. You can reference these easily, for example:
>>> import datetime
>>> daybefore = datetime.timedelta(days=1)
>>> dayminus2 = datetime.timedelta(days=2, minutes=60)
>>> daybefore.days
1
>>> dayminus2.days, dayminus2.seconds
(2, 3600)
To get minutes you're going to have to divide seconds by 60.
来源：https://stackoverflow.com/questions/5006258/need-the-average-from-a-list-of-timedelta-objects