There are a number of built-in functions that can be used on lists that allow you to quickly look through a list without writing your own loops:
>>> nums = [3, 41, 12, 9, 74, 15]>>> print len(nums)6>>> print max(nums)74>>> print min(nums)3>>> print sum(nums)154>>> print sum(nums)/len(nums)25
The sum() function only works when the list elements are numbers. The other functions (max(), len(), etc.) work with lists of strings and other types that can be comparable.
We could rewrite an earlier program that computed the average of a list of numbers entered by the user using a list.
First, the program to compute an average without a list:
total = 0count = 0while ( True ) : inp = raw_input('Enter a number: ') if inp == 'done' : break value = float(inp) total = total + value count = count + 1 average = total / countprint 'Average:', average
In this program, we have count and sum variables to keep the number and running total of the user’s numbers as we repeatedly prompt the user for a number.
We could simply remember each number as the user entered it and use built-in functions to compute the sum and count at the end.
numlist = list()while ( True ) : inp = raw_input('Enter a number: ') if inp == 'done' : break value = float(inp) numlist.append(value) average = sum(numlist) / len(numlist)print 'Average:', average
We make an empty list before the loop starts, and then each time we have a number, we append it to the list. At the end of the program, we simply compute the sum of the numbers in the list and divide it by the count of the numbers in the list to come up with the average.