Example recursion functions

recursion.py

def sum(arr):
  if not arr:
    return 0
  return arr.pop(0) + sum(arr)
  
def count(arr):
  if not arr:
    return 0
  return 1+count(arr[1:])
  
def max(arr, high):
'''
  TODO https://stackoverflow.com/questions/12711397/python-recursive-function-to-find-the-largest-number-in-the-list
'''
  if not arr:
    return high
  tmp = arr.pop(0)
  if tmp > high:
    return max(arr, tmp)
  else:
    return max(arr, high)