状态和行动形式主义。如何在不同类之间实现 +、-、= 运算符

Question

我对一组状态有疑问。要从一种状态转移到另一种状态，我需要执行一组操作。我正在尝试以下列比较 returns 为真：

的方式实施状态和操作类

state1 + actions == state2
state2 - actions == state1
state2 - state1 == actions

我为我的实现编写了一个测试用例，如下所示：

class State:
    pass

class Actions:
    pass

starting_state ={'a':'1',
                 'b':'2'}

some_actions = {'a': 'remove 1',
                'b' : 'remove 2,add #',
                'c' : 'add 5'}
inverse_actions = {'a': 'add 1',
                   'b' : 'remove #,add 2',
                   'c' : 'remove 5'}
final_state = {'b':'#',
               'c':'5'}

state1 = State(starting_state)

actions = Actions(some_actions)

state2= state1 + actions

assert State(final_state)==state2
assert Actions(inverse_actions)== -actions
assert state2 - actions == state1
assert state2 - state1 == actions

我的问题是：

没有任何预建的东西可以帮助我实现状态和动作类?
如果不是，如何实现不同类之间的+和-操作？有没有办法避免循环依赖？

感谢您的帮助！

Answer 1

您可以为此使用运算符重载。这是一个例子：

class A:
    def __init__(self, a):
        self.a = a 

    def __add__(self, other):
        return A(self.a+other.a)

    def __str__(self):
        return str(self.a)
i = A(1)
j = A(1)
l = i+j
assert str(l) == "2"

您可以在此处找到可以根据需要重载的运算符列表： https://docs.python.org/3/library/operator.html

Answer 2

正如 Marin 所建议的，您需要使用运算符重载。这是一个适用于 + 和 == 运算符的简单示例：

class State:
    def __init__(self, s):
        self.state = s

    def __add__(self, other):
        d = self.state.copy()
        if isinstance(other, State):
            d.update(other.state)
        elif isinstance(other, Actions):
            for var, actions in other.actions.items():
                for action in actions.split(","):
                    statement, value = action.split()
                    if statement == "remove":
                        if d.pop(var, None) is None:
                            print("Cannot remove", value, ", not in state")
                    elif statement == "add":
                        d[var] = value
        else:
            return NotImplemented
        return State(d)

    def __eq__(self, other):
        if isinstance(other, State):
            return self.state == other.state
        elif isinstance(other, dict):
            return self.state == other
        else:
            return NotImplemented


class Actions:
    def __init__(self, a):
        self.actions = a


starting_state = {'a': '1',
                  'b': '2'}

some_actions = {'a': 'remove 1',
                'b': 'remove 2,add #',
                'c': 'add 5'}
inverse_actions = {'a': 'add 1',
                   'b': 'remove #,add 2',
                   'c': 'remove 5'}
final_state = {'b': '#',
               'c': '5'}

state1 = State(starting_state)

actions = Actions(some_actions)

state2 = state1 + actions

assert State(final_state) == state2
assert state1 + actions == final_state
# assert Actions(inverse_actions) == -actions
# assert state2 - actions == state1
# assert state2 - state1 == actions

您需要重载 __sub__ 和 __neg__ 才能获得最终结果。

状态和行动形式主义。如何在不同类之间实现 +、-、= 运算符

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状态和行动形式主义。如何在不同 类 之间实现 +、-、= 运算符

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状态和行动形式主义。如何在不同类之间实现 +、-、= 运算符