Sum / Average an attribute of a list of objects

Question

Lets say I have class C which has attribute a .

What is the best way to get the sum of a from a list of C in Python?

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I've tried the following code, but I know that's not the right way to do it:

for c in c_list:
    total += c.a

Answer 1

使用生成器表达式：

sum(c.a for c in c_list)

Answer 2

If you are looking for other measures than sum, eg mean/standard deviation, you can use NumPy and do:

mean = np.mean([c.a for c in c_list])
sd = np.std([c.a for c in c_list])

Answer 3

I had a similar task, but mine involved summing a time duration as your attribute ca . Combining this with another question asked here , I came up with

sum((c.a for c in cList), timedelta())

Because, as mentioned in the link, sum needs a starting value.

Answer 4

Use built-in statistics module:

import statistics

statistics.mean((o.val for o in my_objs))