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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 _show_previous_blank_lines(block):
 """ Show the block previous blank lines """

        # set previous blank lines visibles
        pblock = block.previous()
        while (pblock.text().strip() == '' and
               pblock.blockNumber() >= 0):
            pblock.setVisible(True)
            pblock = pblock.previous()