Convert Number to Roman Numeral and Vice Versa up to 5000 using Python

#Name: Mark Jason T. Galang
#School: FEU-TECH
#Machine Problem number - 3

class RomanNumerals:
  def __init__(self):
    # constructor
    self.res1 = ""
    self.res2 = 0

  def convert_to_roman(self, num):
    """
    this function converts an integer to roman numerals
    """
    # roman numeral symbols
    thousands = ["M", "MM", "MMM", "MMMM", "V̅"]
    hundreds = ["C", "CC", "CCC", "CD", "D" ,"DC", "DCC", "DCCC", "CM"]
    tens = ["X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"]
    ones = ["I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"]

    # conversion using recursion
    # process: divide the number by its place value
    # and store the corresponding roman numeral symbols
    # using the (leading digit - 1) (0-based)
    if num >= 1000:
      self.res1 += thousands[(num // 1000) - 1]
      if num % 1000 != 0:
        return self.convert_to_roman(num % 1000)
      else:
        return self.res1
    elif num >= 100:
      self.res1 += hundreds[(num // 100) - 1]
      if num % 100 != 0:
        return self.convert_to_roman(num % 100)
      else:
        return self.res1
    elif num >= 10:
      self.res1 += tens[(num // 10) - 1]
      if num % 10 != 0:
        return self.convert_to_roman(num % 10)
      else:
        return self.res1
    else:
      self.res1 += ones[num - 1]
      return self.res1

  def convert_to_number(self, rom):
    """
    this function converts roman numerals to an integer
    """

    # roman numeral symbols and their equivalents
    thousands = {"M":1000, "MM":2000, "MMM":3000, "MMMM":4000, "V̅":5000}
    hundreds = {"C":100, "CC":200, "CCC":300, "CD":400, "D":500, "DC":600, "DCC":700, "DCCC":800, "CM":900}
    tens = {"X":10, "XX":20, "XXX":30, "XL":40, "L":50, "LX":60, "LXX":70, "LXXX":80, "XC":90}
    ones = {"I":1, "II":2, "III":3, "IV":4, "V":5, "VI":6, "VII":7, "VIII":8, "IX":9}

    # reverse the dictionaries (using list technique)
    thousands = dict(reversed(list(thousands.items())))
    hundreds = dict(reversed(list(hundreds.items())))
    tens = dict(reversed(list(tens.items())))
    ones = dict(reversed(list(ones.items())))

    # conversion (linear-search)
    # for thousands place
    if len(rom) > 0:
      if rom[0] == "M":
        for th in thousands:
          if th in rom:
            self.res2 += thousands[th]
            rom = rom[len(th):]
            break

    # for hundreds place
    if len(rom) > 0:
      if rom[0] == "C" or rom[0] == "D":
        for h in hundreds:
          if h in rom and h != "D":
            self.res2 += hundreds[h]
            rom = rom[len(h):]
            break
        if len(rom) > 0:
          if "D" in rom:
            self.res2 += hundreds["D"]
            rom = rom[1:]

    # for tens place
    if len(rom) > 0:
      if rom[0] == "X" or rom[0] == "L":
        for t in tens:
          if t in rom and t != "L":
            self.res2 += tens[t]
            rom = rom[len(t):]
            break
        if len(rom) > 0:
          if "L" in rom:
            self.res2 += tens["L"]
            rom = rom[1:]

    # for ones place
    if len(rom) > 0:
      if rom[0] == "I" or rom[0] == "V":
        for o in ones:
          if o in rom and o != "V":
            self.res2 += ones[o]
            rom = rom[len(o):]
            break
        if len(rom) > 0:
          if "V" in rom:
            self.res2 += ones["V"]
            rom = rom[1:]

    return (self.res2 if len(rom) == 0 else 0)

def main():
  while True:
    # menu
    print("MENU\n")
    print("1. convert an integer to a roman numeral")
    print("2. convert a roman numeral to an integer")
    print("3. exit\n")

    # menu - input with error-handling
    ch = eval(input("Enter your choice:"))
    if ch < 1 or ch > 3:
      print("INVALID INPUT: Select from 1 to 3 only.\n")
      continue
    elif type(ch) != int:
      print("INVALID INPUT: Whole number only.\n")
      continue

    if ch == 1:
      # two (2) cases for both input and output
      inp1 = "Enter Integer - "
      inp2 = "EnterInteger - "
      output1 = "Output in Roman numerals is: {0}\n"
      output2 = "Output in Roman Numberals is {0}\n"

      for i in range(2):
        # choice 1 - input with error handling
        n = 0
        while True:
          n = eval(input(inp1 if (i + 1) & 1 else inp2))
          if n <= 0 or n > 5000:
            print("INVALID INPUT: Select from 1 to 5000 only.\n")
            continue
          elif type(n) != int:
            print("INVALID INPUT: Whole number only.\n")
            continue
          else:
            break

        # object instantiation
        rn = RomanNumerals()

        # output
        ans = rn.convert_to_roman(n)
        print(output1.format(ans) if (i + 1) & 1 else output2.format(ans))
    elif ch == 2:
      # two (2) cases for both input and output
      inp1 = "Enter roman numeral - "
      inp2 = "Enter roman numberals - "
      output1 = "Output in Integer is - {0}\n"
      output2 = "Output in Integer is - {0}\n"

      for i in range(2):
        rom = ""
        while True:
          # choice 2 - input with error handling
          rom = str(input(inp1 if (i + 1) & 1 else inp2))
          rom = rom.upper()

          # object instantiation
          rn = RomanNumerals()
          ans = rn.convert_to_number(rom)

          # output with error-handling
          if ans != 0:
            print(output1.format(ans) if (i + 1) & 1 else output2.format(ans))
            break
          else:
            print("INVALID INPUT: Please try again.\n")
            continue

    else:
      print("Program Exiting...")
      break

main()