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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 local_file(self, filename):
 """Read the local file in _self.runway_dir_. Args: filename (str):
 Name of file to retrieve relative to root of _runway_dir_. Returns: str: Contents of local file. Raises: FileNotFoundError: Requested file missing. """

        LOG.info('Retrieving "%s" from "%s".', filename, self.runway_dir)

        file_contents = ''

        file_path = os.path.join(self.runway_dir, filename)

        try:
            with open(file_path, 'rt') as lookup_file:
                file_contents = lookup_file.read()
        except FileNotFoundError:
            LOG.warning('File missing "%s".', file_path)
            raise

        LOG.debug('Local file contents:\n%s', file_contents)
        return file_contents