python recursive function that prints from 0 to n?

Question

I am trying to write a recursive function that prints from 0 to n, but I have no idea how to do it. I accidentally made one that prints from

Answer 1

You almost got it! here's a fixed, simplified version:

def countup(n):
    if n >= 0:
        countup(n - 1)
        print(n)

Notice that:

• You don't have to return anything from a recursive function that only prints values
• For printing in ascending order, the print statement must be placed after the recursive call
• The recursion exits when n < 0, given that we're only printing, there's nothing left to be done afterwards and it's ok to return None (Python's default return value)

UPDATE

It seems that writing a tail recursive solution is all the rage around here :) oh well, here's my shot at it, a simplified and tail-recursive version of @AndyHayden's idea - using the tail call optimization decorator recipe:

@tail_call_optimized
def countup(N, n=0):
    print(n)
    if n < N:
        countup(N, n + 1)

Either way, it works as expected:

countup(5)
=> 0
   1
   2
   3
   4
   5