While teaching recursion in an Introduction to CS class, I wasn't terribly happy with any existing visualizations of recursive methods. I created a very simple command-line vis that traces the calls in sumOfDigits

recursiveTrace.py

'''
ORIGINAL FUNCTION

def sumOfDigits(numberString):
  if len(numberString) < 1:
    return 0
  else:
    return int(numberString[0]) + sumOfDigits(numberString[1:])
'''

def sumOfDigits(numberString, depth=0):
  '''   
  Calculates the sum of a string of digits. 
  Creates a visual trace of the recursion.
  Print assumes that you are using Python 3+ 
  Used in CSCI203 at Bucknell University. 

  input: a string of digits - '2345561'
  output: the sum of the digits (int)
  '''

  if depth == 0:
    print()
    print('Original Call: sumOfDigits(\'' + numberString + '\')\n')

  if len(numberString) < 1:
    return 0

  else:
    simpleStep = int(numberString[0])
    rest = numberString[1:]

    print(' |\t'*depth, simpleStep, '+', 'sumOfDigits(\''+str(rest)+'\')')
    print('\t'*(depth+1), '|')

    compute = sumOfDigits(rest, depth+1)
    answer = simpleStep + compute

    print(' |\t'*depth, simpleStep, '+', compute, '=', answer)
    print('\t'*depth)

    return answer

if __name__ == '__main__':
  # An example of running the function
  sumOfDigits('184323')