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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 iline(self):
 """ Interact with segy in inline mode Returns ------- iline : Line or None Raises ------ ValueError If the file is unstructured Notes ----- .. versionadded:: 1.1 """


        if self.unstructured:
            raise ValueError(self._unstructured_errmsg)

        if self._iline is not None:
            return self._iline

        self._iline = Line(self,
                           self.ilines,
                           self._iline_length,
                           self._iline_stride,
                           self.offsets,
                           'inline',
                          )
        return self._iline