Arithmetic arranger help with code

Hello everyone,
I am stuck with the arithmetic_arranger. I am trying to refactor my code into different functions to make it cleaner, but it seems that there is some issue that I cannot see. Therefore, I would like to ask you for some help on how to refactor it.

Thank you!

Here is the code I wrote:

MAX_PROBLEMS = 5
MAX_LENGTH = 4


def arithmetic_arranger(problems, answer = False):

    # Define variables
    top_line = processing(problems)[0]
    bottom_line = processing(problems)[1]
    dashes = processing(problems)[2]
    results = processing(problems)[3]
    arranged_problems = ""

    # Display the results if answer is True
    if answer == False:
        arranged_problems = '\n'.join((top_line, bottom_line, dashes))
    else:
        arranged_problems = '\n'.join((top_line, bottom_line, dashes, results))

    return arranged_problems


def error_handling(problems, first, operator, second):
  """Function that handles the errors of the Arithmetic Arranger."""

	# Define what happens if len(problems) is larger than 5
  if len(problems) > MAX_PROBLEMS:
    return "Error: Too many problems."

  # Handle length of operands larger than 4
  if len(first) > MAX_LENGTH or len(second) > MAX_LENGTH:
    return "Error: Numbers cannot be more than four digits."

  # Handle no digits in the operands
  elif first.isdigit() == False or second.isdigit() == False:
    return "Error: Numbers must only contain digits."

  # Handle wrong operators, else calculate the results
  elif operator not in ['+','-']:
    return "Error: Operator must be '+' or '-'."

  # If no errors
  else:
    return "No errors."


def processing(problems):
  """Function that processes the problems from the Arithmetic Arranger into the adequate format."""

  # Define variables
  top_list = []
  bottom_list = []
  dashes = []
  results = []

  # Define empty spaces
  empty_space = " " * MAX_LENGTH

  # Extract each problem from the list and split it in three parts
  for problem in problems:
    first, operator, second = problem.split(" ")

    # Pass error_handling function
    error = error_handling(problems, first, operator, second)
    if error != "No errors.":
      return error
              
    # Calculate the maximum width between operands
    width = max(len(first), len(second)) + 2

    # Build top line
    top_list.append(first.rjust(width))

    # Build bottom line
    bottom_list.append(operator + second.rjust(width - 1))

    # Build dashes
    dashes.append('-' * width)

    # Calculate the results for '+' or '-'
    if operator == '+':
      calculations = str(int(first) + int(second))
    elif operator == '-':
      calculations = str(int(first) - int(second))

    # Build results list
    results.append(calculations.rjust(width))             

  # Add empty spaces to the lines
  top_list = empty_space.join(top_list)
  bottom_list = empty_space.join(bottom_list)
  dashes = empty_space.join(dashes)
  results = empty_space.join(results)

  return top_list, bottom_list, dashes, results

The error I am getting is the following:

 python main.py
   32      3801      45      123
+ 698    -    2    + 43    +  49
-----    ------    ----    -----
.FF.FF
======================================================================
FAIL: test_incorrect_operator (test_module.UnitTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/boilerplate-arithmetic-formatter/test_module.py", line 24, in test_incorrect_operator
    self.assertEqual(actual, expected, '''Expected calling "arithmetic_arranger()" with a problem that uses the "/" operator to return "Error: Operator must be '+' or '-'."''')
AssertionError: 'E\nr\nr' != "Error: Operator must be '+' or '-'."
+ Error: Operator must be '+' or '-'.- E
- r
- r : Expected calling "arithmetic_arranger()" with a problem that uses the "/" operator to return "Error: Operator must be '+' or '-'."

======================================================================
FAIL: test_only_digits (test_module.UnitTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/boilerplate-arithmetic-formatter/test_module.py", line 34, in test_only_digits
    self.assertEqual(actual, expected, 'Expected calling "arithmetic_arranger()" with a problem that contains a letter character in the number to return "Error: Numbers must only contain digits."')
AssertionError: 'E\nr\nr' != 'Error: Numbers must only contain digits.'
+ Error: Numbers must only contain digits.- E
- r
- r : Expected calling "arithmetic_arranger()" with a problem that contains a letter character in the number to return "Error: Numbers must only contain digits."

======================================================================
FAIL: test_too_many_digits (test_module.UnitTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/boilerplate-arithmetic-formatter/test_module.py", line 29, in test_too_many_digits
    self.assertEqual(actual, expected, 'Expected calling "arithmetic_arranger()" with a problem that has a number over 4 digits long to return "Error: Numbers cannot be more than four digits."')
AssertionError: 'E\nr\nr' != 'Error: Numbers cannot be more than four digits.'
+ Error: Numbers cannot be more than four digits.- E
- r
- r : Expected calling "arithmetic_arranger()" with a problem that has a number over 4 digits long to return "Error: Numbers cannot be more than four digits."

======================================================================
FAIL: test_too_many_problems (test_module.UnitTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/boilerplate-arithmetic-formatter/test_module.py", line 19, in test_too_many_problems
    self.assertEqual(actual, expected, 'Expected calling "arithmetic_arranger()" with more than five problems to return "Error: Too many problems."')
AssertionError: 'E\nr\nr' != 'Error: Too many problems.'
+ Error: Too many problems.- E
- r
- r : Expected calling "arithmetic_arranger()" with more than five problems to return "Error: Too many problems."

----------------------------------------------------------------------
Ran 6 tests in 0.002s

FAILED (failures=4)

Note how E\nr\nr would be the result of joining the first three characters of Error:... with newlines (you would get E\nr\nr\no if answer were True in any of these tests). You are returning the error message from the error finder to your processing function to your arranger function and it’s treating the message as if it were lines since strings are arrays too.

Yes, you are right, thanks! Certainly, the problem comes when I return the error. But, I cannot find a way to avoid passing it to the arithmetic formatter, unless I use a if/else statement :thinking:

So, I finally solved the issue. Thank you for your help!