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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 _setup_parser(self, filename=None):
 """ Configure the ConfigParser instance the way we want it. Args: filename (str) or None Returns: SafeConfigParser """

        assert isinstance(filename, str) or filename is None

        # If we are not overriding the config filename
        if not filename:
            filename = MACKUP_CONFIG_FILE

        parser = configparser.SafeConfigParser(allow_no_value=True)
        parser.read(os.path.join(os.path.join(os.environ['HOME'], filename)))

        return parser