Why “none”?

def append_sum(lst):
for x in range(3):
lst.append(lst[-1] + lst[-2])

append_sum([1, 1, 2])

The above code gives:

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

why “none”? how will be the correct code using a loop?

Try returning the list, then print it at the caller.

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

A Python function will always have a return value. There is no notion of procedure or routine in Python. So, if you don’t explicitly use a return value in a return statement, or if you totally omit the return statement, then Python will implicitly return a default value for you. That default return value will always be None .
as mtf said put in a return statement.

read more on return here

really appreciate the recommendation, thanks!