I've been running my own statistical analyses, but I'm curious as to why there are different outputs for the following two list comprehensions. I am using Jupyter Notebook on Ubuntu LTS 16.04:

Input: 

```
example = [[15, 16, 17],
           [18, 19, 20]]

list1 = [item[0] + item[1] + item[2] for item in example]

for item in example:

    list2 = [item[0] + item[1] + item[2]]

list1, list2

```

Output: `([48, 57], [57])`

Clearly the second function is printing the sum of the second row, but why not the first?