Sort list of lists based on the sum of each nested list

Question

I am new to python and I am trying to create a function that accepts as input a list of lists of integers and returns a sorted version of that list, sorted by the sum of the integers in each sub-list. Below is the code I have thus far. Any suggestions would be great.

def sort_nested_lists (user_list):
for list in user_list
    x = sum(user_list))
    x = sorted( user_list)
    return x
print sort_nested_lists

Here is my new code:

user_list = raw_input("Please enter a list of integers: ")
def sort_nested_lists(user_list):
  return sorted(user_list,key = sum)
print sort_nested_lists

Now I get the error:

Please enter a list of integers: [[5,2,7,5],[8,2,6,1],[3,1,8,9,5]]

Any additional help would be great!

Answer 1

You do not have to make it so complicated. Simply use the following one-liner :

return sorted(user_list,key=sum)

That's all. When you specify a key , sorted(..) will compare two elements based on the given function it applies to elements in the user_list . So here it will compare two lists based on the sum of their elements.

Answer 2

To achieve this, you may call the sorted function with key as sum

>>> my_list = [[1, 6, 3], [2,1,0], [10, 3, 9]]
>>> sorted(my_list, key=sum)
[[2, 1, 0], [1, 6, 3], [10, 3, 9]]

The resultant list will be sorted in increasing order based on the sum of integers in the sub-lists