在列表中添加数字并追加到新列表

Question

This is what I am trying to do. Create a new list (addtwo) where the each element is the sum of the corresponding and previous elements in a source list (numberlist). Obviously the first element in new list would be same as first element in source list.

numberlist = [2, 4, 5, 1, 8, 2, 0, 1]
addtwo = [el[0] + el[1] for el in numberlist]

Produces this error message: TypeError: 'int' object has no attribute ' getitem '

This is what the new list should look like, using the numbers in "numberlist":

[2, 6, 9, 6, 9, 10, 2, 1]

Answer 1

In your original attempt, el is just an integer, not a list, so trying to index it generated the error message.

You need to iterate over the contents of your original list, compute the sums, and then append those sums to the new list.

Something like this code:

numberlist = [2, 4, 5, 1, 8, 2, 0, 1]
newlist = []
newlist.append(numberlist[0])
for index in range(1,len(numberlist)): 
    sum = numberlist[index] + numberlist[index-1]
    newlist.append(sum)
print 'newlist', newlist

Alternative version using list comprehension, with leading element from original list is

numberlist = [2, 4, 5, 1, 8, 2, 0, 1]
newlist_comp = [numberlist[index] + numberlist[index-1] for index in range(1,len(numberlist))]
newlist_two = numberlist[0] + newlist_comp
print 'newlist_two', newlist_two