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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 to_dis_format(self):
 """Return a string representation of the tree in .dis format."""

        dis_raw_str = self.disfiletree.pformat()
        return re.sub('_!(.*?)_!', join_lines, dis_raw_str, flags=re.DOTALL)