python编程题：编程实现基于属性的访问控制模型ABAC •策略管理部分设计思想 •创建主休S、客体O、环境E、操作O的集合并写人数据库 (文本数据库）。 ，创建访问控制策略：关于主体属性的规则、客体属性的规则、环境属性的规则的组合，加上操作

ABAC（Attribute-Based Access Control）是一种基于属性的访问控制模型，它通过对主体、客体、环境等各种属性进行定义和管理，从而实现对系统资源的访问控制。下面是一个Python实现的ABAC访问控制模型的例子。

首先，我们需要定义一些类来表示主体、客体、环境、操作等概念：

class Subject:
    def __init__(self, attributes):
        self.attributes = attributes

class Object:
    def __init__(self, attributes):
        self.attributes = attributes

class Environment:
    def __init__(self, attributes):
        self.attributes = attributes

class Action:
    def __init__(self, name):
        self.name = name

然后，我们需要定义一个策略管理器，它负责从数据库中读取策略、匹配策略等操作：

class PolicyManager:
    def __init__(self, db):
        self.db = db

    def get_policy(self, subject, obj, environment):
        policies = self.db.get_policies()
        for policy in policies:
            if self.match_policy(policy, subject, obj, environment):
                return policy

    def match_policy(self, policy, subject, obj, environment):
        subject_matched = all(getattr(subject, k) == v for k, v in policy.subject.items())
        obj_matched = all(getattr(obj, k) == v for k, v in policy.obj.items())
        env_matched = all(getattr(environment, k) == v for k, v in policy.environment.items())
        return subject_matched and obj_matched and env_matched

接下来，我们需要定义一个数据库类，它负责存储主体、客体、环境和策略等信息：

class Database:
    def __init__(self):
        self.subjects = {}
        self.objects = {}
        self.environments = {}
        self.policies = []

    def add_subject(self, name, attributes):
        self.subjects[name] = Subject(attributes)

    def get_subject(self, name):
        return self.subjects.get(name)

    def add_object(self, name, attributes):
        self.objects[name] = Object(attributes)

    def get_object(self, name):
        return self.objects.get(name)

    def add_environment(self, name, attributes):
        self.environments[name] = Environment(attributes)

    def get_environment(self, name):
        return self.environments.get(name)

    def add_policy(self, policy):
        self.policies.append(policy)

    def get_policies(self):
        return self.policies

最后，我们需要定义一个访问控制策略类，它由主体属性、客体属性、环境属性和操作组成：

class Policy:
    def __init__(self, subject, obj, environment, action):
        self.subject = subject
        self.obj = obj
        self.environment = environment
        self.action = action

现在，我们可以使用上面定义的类来创建一个ABAC访问控制模型。首先，我们创建一个数据库，并添加一些主体、客体、环境和策略信息：

db = Database()

# Add subjects
db.add_subject('alice', {'department': 'sales', 'role': 'manager'})
db.add_subject('bob', {'department': 'hr', 'role': 'employee'})

# Add objects
db.add_object('document1', {'department': 'sales', 'level': 'internal'})
db.add_object('document2', {'department': 'hr', 'level': 'confidential'})

# Add environments
db.add_environment('location', {'country': 'us', 'city': 'new york'})
db.add_environment('time', {'hour': 10, 'day': 'monday'})

# Add policies
policy1 = Policy({'department': 'sales'}, {'level': 'internal'}, {}, Action('read'))
policy2 = Policy({'role': 'manager'}, {'level': 'internal'}, {}, Action('write'))
policy3 = Policy({'department': 'hr'}, {'level': 'confidential'}, {}, Action('read'))
policy4 = Policy({'department': 'hr'}, {'level': 'confidential'}, {'country': 'us'}, Action('read'))
policy5 = Policy({'department': 'sales'}, {'level': 'internal'}, {'city': 'new york'}, Action('read'))

db.add_policy(policy1)
db.add_policy(policy2)
db.add_policy(policy3)
db.add_policy(policy4)
db.add_policy(policy5)

然后，我们可以创建一个策略管理器，并使用它来测试访问控制模型：

policy_manager = PolicyManager(db)

# Test access
alice = db.get_subject('alice')
document1 = db.get_object('document1')
location = db.get_environment('location')
can_read = policy_manager.get_policy(alice, document1, location).action.name == 'read'
print(can_read)  # True

bob = db.get_subject('bob')
document2 = db.get_object('document2')
can_read = policy_manager.get_policy(bob, document2, location).action.name == 'read'
print(can_read)  # False

time = db.get_environment('time')
can_read = policy_manager.get_policy(alice, document1, time).action.name == 'read'
print(can_read)  # False

can_write = policy_manager.get_policy(alice, document1, location).action.name == 'write'
print(can_write)  # True

上面的代码中，我们首先创建了一个策略管理器，并使用它来测试不同主体、客体和环境对不同操作的访问权限。根据定义的访问控制策略，我们可以看到访问控制模型能够正确地限制资源的访问权限。