Predicting the outcome of recursive calls

Predicting the outcome helps solidify your understanding of recursion. On this page, you are given recursive function definitions, and you will predict what is printed with various invocations.

Example 1. flow

def flow(num):
  if num > 0:
      print('before', num)
      flow (num - 2)
      print('after', num)
  else:
      print('base case')

Your task:

Predict what the flow function prints with these invocations (write it down):

flow(4)

You can see the solution for flow(4) by clicking here.

flow(7)

You can see the solution for flow(7) by clicking here.

Example 2. chop

Note that chop has two recursive calls.

def chop(word):
  if len(word) > 0:
      print(word)
      chop(w[1:])  # 1st recursive call
      print('---')
      chop(w[1:] ) # 2nd recursive call
      print('*')

Your task:

Predict what the chop function prints with this invocation:

chop('mat')

Click here for a diagram of the solution using function call frames.

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