def months_to_reach_target(principal, interest_rate_per_annum, target):
  interest_rate_per_month = (interest_rate_per_annum / 100) / 12
  num_months = 0

  while principal < target
    # I think we can just reassign principal as python references are passed by assignment
    principal += principal * interest_rate_per_month
    num_month += 1

  return num_months

print(months_to_reach_target(100, 10, 200))