Roman Numerals

src/pyBootCamp/roman_numeral_validator.py

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+"""Module to validate Roman Numerals using regular expressions pattern.
+"""
+
+import re
+pattern = '''
+    ^                   # beginning of string
+    M{0,3}              # thousands - 0 to 3 Ms
+    (CM|CD|D?C{0,3})    # hundreds - 900 (CM), 400 (CD), 0-300 (0 to 3 Cs),
+                        #            or 500-800 (D, followed by 0 to 3 Cs)
+    (XC|XL|L?X{0,3})    # tens - 90 (XC), 40 (XL), 0-30 (0 to 3 Xs),
+                        #        or 50-80 (L, followed by 0 to 3 Xs)
+    (IX|IV|V?I{0,3})    # ones - 9 (IX), 4 (IV), 0-3 (0 to 3 Is),
+                        #        or 5-8 (V, followed by 0 to 3 Is)
+    $                   # end of string
+    '''
+
+print(re.search(pattern, 'M', re.VERBOSE))
+# <re.Match object at 0x008EEB48>
+
+print(re.search(pattern, 'MCMLXXXIX', re.VERBOSE))
+# <re.Match object at 0x008EEB48>
+
+print(re.search(pattern, 'MMMDCCCLXXXVIII', re.VERBOSE))
+# <re.Match object at 0x008EEB48>
+
+print(re.search(pattern, "MCMLXXXIX", re.VERBOSE))
+# <re.Match object at 0x008EEB48>
+
+print(re.search(pattern, 'M'))
+# None

src/pyBootCamp/romanconverter.py

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+"""Module to convert integers between 0-3999 from user's input into equivalent Roman Numerals.
+  Stores the Roman Numeral as a string.
+"""
+
+# Integer provided by user.
+number = int(input("Enter a number from 0 to 3999: "))
+
+# Dictionary mapping an integer to equivalent Roman Numeral as a string.
+roman = {
+    1000: "M",
+    900: "CM",
+    500: "D",
+    400: "CD",
+    100: "C",
+    90: "XC",
+    50: "L",
+    40: "XL",
+    10: "X",
+    9: "IX",
+    5: "V",
+    4: "IV",
+    1: "I"
+}
+
+if number > 3999:
+    print("Unable to convert to equivalent Roman Numeral as",
+          number, "is greater than 3999")
+elif number < 0:
+    print("You have entered a negative integer:", number)
+    print("Negative Integers cannot be converted to equivalent Roman Numerals.")
+else:
+    result = ""
+    unit = 1  # One's place initially.
+    while number:
+        """Gather successive digits in the number from right to left.
+          Modulo operator evaluates to a float type. 
+          Convert the value of the operation to int type before storing it in variabe digit.
+          The variable digit is used in integer division with is not compatible with float types.
+        """
+        digit = int(number % 10) * unit
+        if digit == 0:
+            # Unit placeholder one's, ten's, hundered's and thousand's place in an integer.
+            unit *= 10
+            number /= 10
+            continue
+        elif digit > 0 and digit < 4:
+            result = roman[1] * digit + result
+        elif digit == 4:
+            result = roman[digit] + result
+        elif digit >= 5 and digit < 9:
+            result = roman[5] + roman[1] * (digit - 5) + result
+        elif digit == 9:
+            result = roman[digit] + result
+        elif digit >= 10 and digit < 40:
+            result = roman[10] * (digit // unit) + result
+        elif digit == 40:
+            result = roman[digit] + result
+        elif digit >= 50 and digit < 90:
+            result = roman[50] + roman[10] * ((digit - 50) // unit) + result
+        elif digit == 90:
+            result = roman[digit] + result
+        elif digit >= 100 and digit < 400:
+            result = roman[100] * (digit // unit) * result
+        elif digit == 400:
+            result = roman[digit] + result
+        elif digit >= 500 and digit < 900:
+            result = roman[500] + roman[100] * ((digit - 500) // unit) + result
+        elif digit == 900:
+            result = roman[digit] + result
+        else:
+            result = roman[1000] * (digit // unit) + result
+        # Multiply the placeholder by 10 to represent the next digit in the number.
+        unit *= 10
+        # remove the digits from the number from right to left.
+        number /= 10
+    print(result)