Arithmetic Arranger

arithmetic_arranger.py

from problem import ArithmeticProblem

def arithmetic_arranger(problems, show_answer=False):
  try:
    if len(problems) > 5:
      raise ValueError("Too many problems.")

    def convert_problem(s):
      return str(ArithmeticProblem(s, show_answer)).splitlines()

    equations = map(convert_problem, problems)
    zipped_lines = zip(*equations)
    arranged = "\n".join(["    ".join(line) for line in zipped_lines])

    return arranged
  except ValueError as err:
    return f"Error: {err}"

main.py

# This entrypoint file to be used in development. Start by reading README.md
from arithmetic_arranger import arithmetic_arranger
from unittest import main


print(arithmetic_arranger(["32 + 698", "3801 - 2", "45 + 43", "123 + 49"]))


# Run unit tests automatically
main(module='test_module', exit=False)

problem.py

class ArithmeticProblem:
  VALID_OPERATIONS = ('+', '-')

  def __init__(self, problem, show_answer=False):
    value_a, operation, value_b = problem.split()

    if operation not in ArithmeticProblem.VALID_OPERATIONS:
      raise ValueError("Operator must be '+' or '-'.")

    self.operation = operation

    for v in [value_a, value_b]:
      if not v.isnumeric():
        raise ValueError("Numbers must only contain digits.")
      if len(v) > 4:
        raise ValueError("Numbers cannot be more than four digits.")

    self.a = int(value_a)
    self.b = int(value_b)
    self.answer = self.a + self.b if self.operation == "+" else self.a - self.b
    self.show_answer=show_answer

  def __str__(self):
    a_length = len(str(self.a))
    b_length = len(str(self.b))
    longest = a_length if a_length >= b_length else b_length

    s = (
      f"  {(self.a):>{longest}}\n"
      f"{self.operation} {self.b:>{longest}}\n"
      f"--{'-' * longest}"
    )

    if self.show_answer:
      s += f"\n{self.answer:>{longest + 2}}"

    return s