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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def tokenize(self, string):
 """Tokenize a string and return an iterator over its tokens."""

        it = colorise.compat.ifilter(None, self._pattern.finditer(string))

        try:
            t = colorise.compat.next(it)
        except StopIteration:
            yield string, False
            return

        pos, buf, lm, escapeflag = -1, '', -1, False

        # Check if we need to yield any starting text
        if t.start() > 0:
            yield string[:t.start()], False
            pos = t.start()

        it = itertools.chain([t], it)

        for m in it:
            start = m.start()
            e, s = m.group(2) or '', m.group(3)
            escaped = e.count(self._ESCAPE) % 2 != 0

            if escaped:
                buf += string[pos:m.end(2)-1] + s
                escapeflag = True
            else:
                buf += string[pos:m.start(3)]

                if buf:
                    yield buf, escapeflag
                    buf = ''
                    escapeflag = False

                if lm == start:
                    yield '', False

                yield s, False
                lm = m.end()

            pos = m.end()

        if buf:
            yield buf, escapeflag
            escapeflag = False

        if pos < len(string):
            yield string[pos:], False