average of attribute in a list of objects

Question

I have a list of user's. Each user will have a waitTime attribute. How do I get the average waitTime for all users in the list? The code below will probably work, but I'm guessing that there is a better way to do it.

sum = 0
for user in self.done:
    sum += user.waitTime 
sum/len(self.done)

Answer 1

You can use the builtin sum function combined with a generator expression for this.

sum(user.waitTime for user in self.done)/float(len(self.done))

The float is only necessary in python2.x and only if all the user.waitTime objects are integers.

Answer 2

Using a generator expression and sum for the sum:

sum(user.waitTime for user in self.done) / float(len(self.done))

If the times are integers, you need to convert the result from len() into float, otherwise you get integer division, ie truncating in Python 2.