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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_parent_directory_number(self, parent_dir_num):
        # type: (int) -> None
        '''
        A method to update the parent directory number for this Path Table
        Record from the directory record.

        Parameters:
         parent_dir_num - The new parent directory number to assign to this PTR.
        Returns:
         Nothing.
        '''
        if not self._initialized:
            raise pycdlibexception.PyCdlibInternalError('Path Table Record not yet initialized')
        self.parent_directory_num = parent_dir_num