Roman numeral encoding, based on XKCD#2637

romanencoder.py

import re
from PyQt5.QtWidgets import (QApplication, QVBoxLayout, QWidget, QLabel, QTextEdit)

'''
Inspired by https://xkcd.com/2637/
Based on the Python code of tools/roman.py
'''

RomanNumbers = 'ivxlcdmIVXLCDM'

NumberToRoman = (
    (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'),
)
RomanToNumber = tuple((v, k) for k, v in NumberToRoman)
RomanRegex = re.compile(r'm*(cm|cd|d?c{0,3})(xc|xl|l?x{0,3})(ix|iv|v?i{0,3})')


def romanToDigits(values):
    result = 0
    index = 0
    for numeral, integer in RomanToNumber:
        while values[index:index+len(numeral)].lower() == numeral.lower():
            result += integer
            index += len(numeral)
    result = str(result)
    if index < len(values):
        result += romanToDigits(values[index:])
    return result

def romanEncode(roman):
    result = ''
    current = ''
    for l in roman:
        if l in RomanNumbers:
            current += l
        else:
            if current:
                result += romanToDigits(current)
                current = ''
            result += l
    if current:
        result += romanToDigits(current)
    return result


def digitsToRoman(value):
    roman = ''
    for n, r in NumberToRoman:
        fact, value = divmod(value, n)
        roman += r * fact
        if not value:
            break
    return roman

def romanDecode(text):
    result = ''
    tempNumber = ''
    for l in text:
        if l.isdigit():
            tempNumber += l
        else:
            if tempNumber:
                result += digitsToRoman(int(tempNumber))
            result += l
            tempNumber = ''
    if tempNumber:
        result += digitsToRoman(int(tempNumber))
    return result


class EncodeMMDCXXXVII(QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)
        layout = QVBoxLayout(self)
        sourceLabel = QLabel('Source')
        layout.addWidget(sourceLabel)
        self.sourceEdit = QTextEdit()
        sourceLabel.setBuddy(self.sourceEdit)
        layout.addWidget(self.sourceEdit)

        encodeLabel = QLabel('Encoded')
        layout.addWidget(encodeLabel)
        self.encodedEdit = QTextEdit()
        encodeLabel.setBuddy(self.encodedEdit)
        layout.addWidget(self.encodedEdit)

        decodeLabel = QLabel('Decoded')
        layout.addWidget(decodeLabel)
        self.decodedEdit = QTextEdit(readOnly=True)
        decodeLabel.setBuddy(self.decodedEdit)
        layout.addWidget(self.decodedEdit)

        self.sourceEdit.textChanged.connect(self.encode)
        self.encodedEdit.textChanged.connect(self.decode)

    def encode(self):
        self.encodedEdit.setText(
            romanEncode(self.sourceEdit.toPlainText()))

    def decode(self):
        self.decodedEdit.setText(
            romanDecode(self.encodedEdit.toPlainText()))


if __name__ == '__main__':
    import sys
    app = QApplication(sys.argv)
    win = EncodeMMDCXXXVII()
    win.show()
    sys.exit(app.exec_())