Fibonacci function with list comprehension returns None

Returns [None,None,None,None,None]

def perimeter(num):
    lst = [1]
    return [lst.append(n+lst[lst.index(n)-1]) for n in lst if len(lst) <= num]

print(perimeter(5))

>Solution :

lst.append(...) doesn’t return anything (more precisely, returns None).

Your function returns the list created with the list comprehenshion . This list contains 5 results of lst.append(...) – which are all None.

What you technically can do, is return lst from the function:

def perimeter(num):
    lst = [1]
    [lst.append(n+lst[lst.index(n)-1]) for n in lst if len(lst) <= num]
    return lst

print(perimeter(5))
[1, 2, 3, 5, 8, 13]