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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 replaceText(self, pos, length, text):
 """Replace length symbols from ``pos`` with new text. If ``pos`` is an integer, it is interpreted as absolute position, if a tuple - as ``(line, column)`` """

        if isinstance(pos, tuple):
            pos = self.mapToAbsPosition(*pos)

        endPos = pos + length

        if not self.document().findBlock(pos).isValid():
            raise IndexError('Invalid start position %d' % pos)

        if not self.document().findBlock(endPos).isValid():
            raise IndexError('Invalid end position %d' % endPos)

        cursor = QTextCursor(self.document())
        cursor.setPosition(pos)
        cursor.setPosition(endPos, QTextCursor.KeepAnchor)

        cursor.insertText(text)