I'm a bit stuck in python

Question

So i have to write a function that adds the sum of the two last numbers in a list together and adds this sum to the list. I have to do this 3 times, i could either do it without a loop or with a loop, i chose to do the difficult path, because i want to challenge myself, but i'm a bit stuck.

When i run the code with input print(append_sum([1, 1, 2])) it returns the correct value, but when i input print(append_sum([2, 5])) it only return 2, 5, 7

Full code is below:

#Write your function here
def append_sum(lst):
  i = 0
  for i in lst:
    lst.append(lst[-1] + lst[-2])
    i += 1
    if i == 3:
      return lst

#Uncomment the line below when your function is done
print(append_sum([1, 1, 2]))

Answer 1

You need not iterate every item in list.

def append_sum(lst):
    repetitions = 3
    for i in range(repetitions):
        lst.append(lst[-1] + lst[-2])
    return lst

print(append_sum([1, 1, 2]))

Output:

[1, 1, 2, 3, 5, 8]

Answer 2

You are overwriting i variable in the for loop. Change the name to a different variable.

#Write your function here
def append_sum(lst):
  counter = 0
  for i in lst:
    lst.append(lst[-1] + lst[-2])
    counter += 1
    if counter == 3:
      return lst

#Uncomment the line below when your function is done
print(append_sum([1, 1, 2]))

It is generally a really bad practice to use a, b, c, x, y, z, i, j, k etc as variable names, as it makes the code less readable. Please use better variable names.

# Write your function here
def append_sum(numbers_list):
    counter = 0
    for number in numbers_list:
        numbers_list.append(numbers_list[-1] + numbers_list[-2])
        counter += 1
        if counter == 3:
            return numbers_list


# Uncomment the line below when your function is done
print(append_sum([2, 5]))

In fact, for this case, you don't even need to iterate over the list.

# Write your function here
def append_sum(numbers_list):
    if len(numbers_list) < 2:
        raise Exception("List must have at least two numbers")

    for counter in range(1, 3 + 1):
        numbers_list.append(numbers_list[-1] + numbers_list[-2])
        if counter == 3:
            return numbers_list


# Uncomment the line below when your function is done
print(append_sum([1, 1, 2]))