解决Python PDDL框架中的RecursionError：正确定义动作效果

from pddl.logic import Predicate, variables
from pddl.core import Domain, Problem
from pddl.action import Action
from pddl.formatter import domain_to_string, problem_to_string
from pddl.requirements import Requirements

class TSPBasic:
    def __init__(self, connections, start_city):
        self.connections = connections
        self.start_city = start_city

        unique_cities = set()
        for start, end in connections:
            unique_cities.update([start, end])
        # 将所有城市定义为position类型的变量
        self.cities = variables(" ".join(unique_cities), types=["position"])

        # 定义动作中使用的单个城市变量
        self.start = variables("start", types=["position"])[0]
        self.finish = variables("finish", types=["position"])[0]

        # 定义谓词
        self.at = Predicate("at", self.start)
        self.connected = Predicate("connected", self.start, self.finish)
        self.visited = Predicate("visited", self.finish)

        self.domain = self.create_domain()
        self.problem = self.create_problem()

# 错误的代码示例
effect="&".join([
    str(self.at(self.finish)),
    str(self.visited(self.finish)),
    "~" + str(self.at(self.start))
])

# 正确的代码示例
def create_actions(self):
    move = Action(
        "move",
        parameters=[self.start, self.finish],
        precondition=self.at(self.start) &
                     self.connected(self.start, self.finish) &
                     ~self.visited(self.finish),
        effect=self.at(self.finish) & self.visited(self.finish) & ~self.at(self.start)
    )
    return [move]

# tsp_basic.py 中的 create_domain 方法
def create_domain(self):
    # 明确声明所需的需求，例如STRIPS, TYPING, NEG_PRECONDITION
    requirements = [Requirements.STRIPS, Requirements.TYPING, Requirements.NEG_PRECONDITION]

    domain = Domain(
        "tsp_basic_domain",
        requirements=requirements,
        types={"position": None}, # 定义position类型
        constants=[], # 本例中没有全局常量
        predicates=[self.at, self.connected, self.visited], # 注册所有谓词
        actions=self.create_actions() # 注册所有动作
    )
    return domain

# tsp_basic.py 中的 create_problem 方法
def create_problem(self):
    requirements = [Requirements.STRIPS, Requirements.TYPING]

    # 将所有唯一城市作为问题对象
    objects = self.cities

    # 定义初始状态
    init = [self.at(variables(self.start_city, types=["position"])[0])] # 初始位于起始城市
    for start, finish in self.connections:
        # 添加所有城市连接关系
        init.append(self.connected(variables(start, types=["position"])[0],
                                   variables(finish, types=["position"])[0]))

    # 定义目标状态：所有城市被访问且最终回到起始城市
    goal_conditions = [self.visited(city) for city in self.cities if city.name != self.start_city]
    goal_conditions.append(self.at(variables(self.start_city, types=["position"])[0]))
    # 同样，这里也需要使用逻辑运算符，而非字符串拼接
    goal = goal_conditions[0]
    for cond in goal_conditions[1:]:
        goal &= cond

    problem = Problem(
        "tsp_basic_problem",
        domain=self.domain,
        requirements=requirements,
        objects=objects,
        init=init,
        goal=goal
    )
    return problem

# main.py
from tsp_basic import TSPBasic
import subprocess

# 定义城市连接和起始城市
connections = [("Boston", "NewYork"), ("NewYork", "Boston"), ...]
start_city = "NewYork"

# 实例化TSPBasic类，它会自动构建Domain和Problem对象
tsp = TSPBasic(connections, start_city)

# 获取PDDL域和问题的字符串表示
domain_pddl_str = tsp.get_domain()
problem_pddl_str = tsp.get_problem()

# 将PDDL字符串保存到文件
with open('domain.pddl', 'w') as domain_file:
    domain_file.write(domain_pddl_str)
with open('problem.pddl', 'w') as problem_file:
    problem_file.write(problem_pddl_str)

# 定义并执行Fast-Downward命令
command = ["/home/mihai/tools/downward/fast-downward.py", "./domain.pddl", "./problem.pddl",
           "--heuristic", "h=ff()", "--search", "astar(h)"]

process = subprocess.run(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True)

# 检查执行结果
if process.returncode == 0:
    print("Command executed successfully!")
    print(process.stdout)
else:
    print("Error in command execution.")
    print("Error Output:\n", process.stderr)