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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 backspace(self):
 """ Moves the cursor one place to the left, erasing the character at the current position. Cannot move beyond column zero, nor onto the previous line. """

        if self._cx + self._cw >= 0:
            self.erase()
            self._cx -= self._cw

        self.flush()