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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 grid_file_path(self):
 """Validate that grid file path points to a file. :return: The grid xml file path. :rtype: str :raises: GridXmlFileNotFoundError """

        if os.path.isfile(self.grid_xml_path):
            return self.grid_xml_path
        else:
            raise GridXmlFileNotFoundError