如何在单独的文件中访问类外部定义的变量，而不会遇到循环导入？-解网

问：

我想访问在类的实例中定义的。这是我的代码my_variablemain.pySecondThread

main.py

import threading
import time
import signal
import traceback

from second_thread import SecondThread
from first_thread import FirstThread

my_variable = threading.Event()

def stop_handler(signum, frame):
    print(f"Signal received: {signum}")
    print(f"Stack frame:\n{traceback.print_stack(frame)}")
    global my_variable
    print("Setting my_variable...")
    my_variable.set()
    print(f"my_variable[{threading.get_native_id()}]:: {my_variable}")
    time.sleep(5)
    print("Unsetting my_variable...")
    my_variable.clear()
    print(f"my_variable[{threading.get_native_id()}]:: {my_variable}")

def start():
    signal.signal(signal.SIGTERM, stop_handler)
    signal.signal(signal.SIGINT, stop_handler)

    print(f"my_variable[{threading.get_native_id()}]: {my_variable}")

    first_thread = threading.Thread(target=FirstThread().run, daemon=True, name='FirstThread')
    first_thread.start()

    second_thread = threading.Thread(target=SecondThread().run, daemon=True, name='SecondThread')
    second_thread.start()

    while True:
        first_thread.join(1)

if __name__ == "__main__":
    start()

first_thread.py

import threading
import time

from second_thread import SecondThread

class FirstThread:
    def __init__(self):
        print(f"FirstThread[{threading.get_native_id()}]: Started")

    def run(self):
        for x in range(100):
            if 'SecondThread' in [t.name for t in threading.enumerate()]:
                print(f"{x}/100 FirstThread[{threading.get_native_id()}]: Sleeping for 10 seconds")
            else:
                print(f"{x}/100 FirstThread[{threading.get_native_id()}]: SecondThread is not running yet...")
                print(f"{x}/100 FirstThread[{threading.get_native_id()}]: Waiting 5 seconds and checking again...")
                time.sleep(5)
                if not 'SecondThread' in [t.name for t in threading.enumerate()]:
                    print(f"{x}/100 FirstThread[{threading.get_native_id()}]: Starting SecondThread again...")
                    second_thread = threading.Thread(target=SecondThread().run, daemon=True, name='SecondThread')
                    second_thread.start()
                else:
                    print(f"{x}/100 FirstThread[{threading.get_native_id()}]: SecondThread instance was found!")

            time.sleep(10)
        print(f"FirstThread[{threading.get_native_id()}]: Exiting...")

second_thread.py

import threading
import time

from main import my_variable

class SecondThread:
    def __init__(self):
        print(f"SecondThread[{threading.get_native_id()}]: Started")

    def run(self):
        for x in range(100):
            if not my_variable.is_set():
                print(f"{x}/100 SecondThread[{threading.get_native_id()}]: Sleeping for 10 seconds")
                time.sleep(10)
        print(f"SecondThread[{threading.get_native_id()}]: Exiting...")

如果我运行，我会得到：python3 main.py

ImportError: cannot import name 'SecondThread' from partially initialized module 'second_thread' (most likely due to a circular import) (/home/ubuntu/test/second_thread.py)

如果我删除并在 in second_thread.py之前添加一个右键，我会得到：from main import my_variableglobal my_variableif not my_variable.is_set():

NameError: name 'my_variable' is not defined

如果我在单个 main.py 文件中定义所有线程类，而不是将它们放在单独的文件中，这将起作用，但我不想这样做。

我怎样才能避免这种情况？

python-3.x 类变量作用域 python-multithreading

然而，在这种情况下，当主程序运行时，它是由解释器以名称而不是 “导入”的，所以当时，导入系统找不到导入缓存中指定的模块，因此继续再次导入主模块，创建另一个对象，该对象不与主程序运行时创建的对象共享。__main__mainsecond_thread.pyimport mainmainEvent

因此，要访问解释器最初加载的主模块，您需要指定名称：__main__

second_thread.py

import threading
import time
import sys    

class SecondThread:
    def __init__(self):
        print(f"SecondThread[{threading.get_native_id()}]: Started")

    def run(self):
        from __main__ import my_variable

        for x in range(100):
            if not my_variable.is_set():
                print(f"{x}/100 SecondThread[{threading.get_native_id()}]: Sleeping for 10 seconds")
                time.sleep(10)
        print(f"SecondThread[{threading.get_native_id()}]: Exiting...")

此外，你不必要地在打电话后打电话，所以又变成了。删除调用，程序将按预期工作。my_variable.clear()my_variable.set()my_variable.is_set()False

演示：https://replit.com/@blhsing/BitterAdmirableStructs

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如何在单独的文件中访问类外部定义的变量，而不会遇到循环导入？

How do I access a variable defined outside my class in a separate file without running into circular imports?

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