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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 update_spec(self):
 """Update the source specification with information from the row intuiter, but only if the spec values are not already set. """


        if self.datafile.exists:
            with self.datafile.reader as r:

                self.header_lines = r.info['header_rows']
                self.comment_lines = r.info['comment_rows']
                self.start_line = r.info['data_start_row']
                self.end_line = r.info['data_end_row']