Lists addition

Question

Why does
nums=[1,2,3]
print(nums+[4,5,6])

Does not print

5,7,8?
Instead it does
1,2,3,4,5,6

Answer 1

The + operator on list-type collections (e.g., lists, strings) means "concatenation".

When you concatenate two or more lists, you obtain a new list composed by their elements in the same order you expressed the concatenation.

Thus:
[1, 2, 3] + [4, 5, 6] gives you [1, 2, 3, 4, 5, 6]

If you want to obtain a more "algebraic" result you have to consider using NumPy or implement a new class that wraps lists and overloads the __add__ method.

Answer 2

because you are doing operation on lists not on integer variable !

Answer 3

you're telling your pc to print the list nums First (1,2,3) and then to print the list 4,5,6 so the result is 1,2,3,4,5,6

Answer 4

raw.input() might work as in some programs it adds all the values in the list and gives the sum as result

Answer 5

Basically + operator over 2 list will just append the content of the second list, by this way it jus creates and does not change original list until and unless we mention. Also extend() is a built in function that does the same job, but it changes the list upon which it is called.For example:
list1 = [1, 2, 3]
list2 = [4, 5, 6]
list1.extend(list2) # will change the list1 now
print(l1) #[1,2,3,4,5,6]

If you want to add each element on the list to another list's corresponding values, you should make use map function like this
list1 = [1, 2, 3]
list2 = [4, 5, 6]
print(map(lambda x,y: x+y, list1, list2))

# this will print
# [5, 7, 9]