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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 file_name(self, value):
 """The filename of the attachment :param file_name: The filename of the attachment :type file_name: FileName, string """

        if isinstance(value, FileName):
            self._file_name = value
        else:
            self._file_name = FileName(value)