Regex #1

regex01.py

import term


exp = '(+|-|e)dd*'


class InvalidInput(ValueError):
    pass


class Matcher(object):
    def __init__(self, text):
        self.pos = 0
        self.text = text

    def match(self):
        cursor = self.read()
        try:
            ch = next(cursor)

            if ch == '+' or ch == '-':
                ch = next(cursor)

            if ch.isdigit():
                while True:
                    try:
                        ch = next(cursor)
                    except StopIteration:
                        break
                    if not ch.isdigit():
                        self.error('Number should contain only digits')

            else:
                self.error('Number should start with a digit')
                
        except StopIteration:
            self.error('Unexpected end of input')

    def read(self):
        for pos, char in enumerate(self.text):
            self.pos = pos
            yield char

    def error(self, message):
        term.writeLine('Error at position {pos}: {message}'.format(
            pos=self.pos, message=message), term.red)
        term.writeLine(self.text)
        term.write('-'*self.pos, term.yellow)
        term.write('^\n', term.yellow)
        raise InvalidInput(message)


def main():
    valid_input = '-234532'
    invalid_input = '+235235d323'
    m1 = Matcher(valid_input)
    m1.match()
    m2 = Matcher(invalid_input)
    m2.match()


if __name__ == '__main__':
    main()