input: def int_to_Roman(number: int) -> str:
      """
      Convert a given number into its Roman form.
  
      >>> int_to_Roman(15)
      'XV'
      >>> int_to_Roman(2021)
      'MMXXI'
      >>> int_to_Roman(94)
      'XCIV'
      >>> int_to_Roman(3999)
      'MMMCMXCIX'
      """
      val = [
          1000, 900, 500, 400,
          100, 90, 50, 40,
          10, 9, 5, 4,
          1
      ]
      syb = [
          "M", "CM", "D", "CD",
          "C", "XC", "L", "XL",
          "X", "IX", "V", "IV",
          "I"
      ]
      roman_num = ''
      i = 0
      while number > 0:
          for_val = number // val[i]
          roman_num += syb[i] * for_val
          number -= val[i] * for_val
          i += 1
      return roman_num
output:     val = [
          1000, 900, 500, 400,
          100, 90, 50, 40,
          10, 9, 5, 4,
          1
      ]
      syb = [
          "M", "CM", "D", "CD",
          "C", "XC", "L", "XL",
          "X", "IX", "V", "IV",
          "I"
      ]
      roman_num = ''
      i = 0
      while number > 0:
          for_val = number // val[i]
          roman_num += syb[i] * for_val
          number -= val[i] * for_val
          i += 1
      return roman_num