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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 init(policy_file=None, rules=None, default_rule=None, use_conf=True):
 """Init an Enforcer class. :param policy_file: Custom policy file to use, if none is specified, `CONF.policy_file` will be used. :param rules: Default dictionary / Rules to use. It will be considered just in the first instantiation. :param default_rule: Default rule to use, CONF.default_rule will be used if none is specified. :param use_conf: Whether to load rules from config file. """


    global _ENFORCER
    global saved_file_rules

    if not _ENFORCER:
        _ENFORCER = policy.Enforcer(CONF,
                                    policy_file=policy_file,
                                    rules=rules,
                                    default_rule=default_rule,
                                    use_conf=use_conf
                                    )
        register_rules(_ENFORCER)
        _ENFORCER.load_rules()
    # Only the rules which are loaded from file may be changed
    current_file_rules = _ENFORCER.file_rules
    current_file_rules = _serialize_rules(current_file_rules)

    if saved_file_rules != current_file_rules:
        _warning_for_deprecated_user_based_rules(current_file_rules)
        saved_file_rules = copy.deepcopy(current_file_rules)