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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 linenum(self, index):
 """Gets the line number of the character at the specified index. If the result is unknown, -1 is returned."""

        if len(self._lines) == 0 and self.refstring != "":
            self._lines = self.refstring.split("\n")
            #Add one for the \n that we split on for each line
            self._chars = [ len(x) + 1 for x in self._lines ]
            #Remove the last line break since it doesn't exist
            self._chars[-1] -= 1

            #Now we want to add up the number of characters in each line
            #as the lines progress so that it is easy to search for the
            #line of a single character index
            total = 0
            for i in range(len(self._chars)):
                total += self._chars[i]
                self._chars[i] = total

        if len(self._lines) > 0:
            #Now, find the first index where the character value is >= index
            result = -1
            i = 0
            while result == -1 and i < len(self._chars):
                if index <= self._chars[i]:
                    result = [ i, self._chars[i] - index]
                i += 1

            return result
        else:
            return [ -1, -1 ]