python - Thead.join() 仅在所有线程完成后才帮助打印字符串

Question

我目前正在尝试编写一个实现以下功能的函数:

• 按随机顺序从“消息”列表中获取所有消息，同时确保没有重复的消息。
• 在延迟 1 - 10 秒范围内的随机秒数后打印它们。
• 所有线程完成后，打印字符串“打印完成，5秒后返回主菜单。”

然而，我遇到的问题是字符串“Printing is finish...”是在随机消息之间打印的，而不是在它们之后。

我的困惑源于这样一个事实:.join() 方法对于类似的函数来说完美无缺。仅在所有线程完成后才打印该字符串。它们之间的主要区别在于另一个函数不接受任何随机输入。相反，它会迭代一个名为“messages_and_times”的全局字典，其中键:值对来自用户输入的消息和秒数(用户输入由另一个函数处理)。

下面您可以看到函数 option_3() 不起作用，而函数 option_2() 起作用。在最底部我将包含整个代码以供进一步引用。

有人可以帮我理解我做错了什么吗？

预先感谢您的时间和帮助。

附注clear() 函数用于在每次输入后清除终端显示。

非工作功能:

def option_3():
    clear()
    messages = ["message_1", "message_2", "message_3", "message_4", "message_5",
                "message_6", "message_7", "message_8", "message_9", "message_10"]

    print("Printing initialized:\n")

    def threading_function(message, seconds):
        time.sleep(seconds)
        print(message)

    for message in messages:
        randomized_messages = []
        random_index = random.randint(0, len(messages) - 1)
        randomized_messages.append(messages.pop(random_index))
        for msg in randomized_messages:
            t = Thread(target=threading_function, args=(msg, random.choice(range(1,11))))
            t.start()


    t.join()
    time.sleep(0.5)
    print(
        "\nPrinting is finished. You will be returned to the main menu in 5 seconds.")
    time.sleep(5)
    main_menu()

<小时/>

工作功能:

def option_2():
    global messages_and_times

    clear()
    print("Printing initialized:\n")

    def threading_function(message, seconds):
        time.sleep(seconds)
        print(message)

    for message, seconds in messages_and_times.items():
        t = Thread(target=threading_function, args=(message, seconds))
        t.start()

    t.join()
    time.sleep(0.5)
    print(
        "\nPrinting is finished. You will be returned to the main menu in 5 seconds.")
    time.sleep(5)
    main_menu()

<小时/>

整个 main_menu() 函数:

import os
import random
clear = lambda: os.system('cls')

messages_and_times = {}


def main_menu():

    def option_1():
        global messages_and_times

        clear()
        message = input(
            "Please type in a message you would like to add to the list:")
        clear()
        seconds = int(
            input("Please type in the time of delay for this message:"))
        messages_and_times[message] = seconds

        def create_dictionary():

            clear()
            answer = input(
                "Would you like to add another message? (yes/no)").lower()
            if answer == "yes":
                option_1()
            elif answer == "no":
                clear()
                print("You will now be returned to the main menu.")
                time.sleep(1.5)
                main_menu()
            else:
                clear()
                print("Please answer yes or no.")
                time.sleep(1.5)
                create_dictionary()
        create_dictionary()

    def option_2():
        global messages_and_times

        clear()
        print("Printing initialized:\n")

        def threading_function(message, seconds):
            time.sleep(seconds)
            print(message)

        for message, seconds in messages_and_times.items():
            t = Thread(target=threading_function, args=(message, seconds))
            t.start()

        t.join()
        time.sleep(0.5)
        print(
            "\nPrinting is finished. You will be returned to the main menu in 5 seconds.")
        time.sleep(5)
        main_menu()

    def option_3():
        clear()
        messages = ["message_1", "message_2", "message_3", "message_4", "message_5",
                    "message_6", "message_7", "message_8", "message_9", "message_10"]
        randomized_messages = []
        print("Printing initialized:\n")

        def threading_function(message, seconds):
            time.sleep(seconds)
            print(message)

        for message in messages:
            random_index = random.randint(0, len(messages) - 1)
            randomized_messages.append(messages.pop(random_index))
        for msg in randomized_messages:
            t = Thread(target=threading_function, args=(msg, random.choice(range(1,11))))
            t.start()


        t.join()
        time.sleep(0.5)
        print(
            "\nPrinting is finished. You will be returned to the main menu in 5 seconds.")
        time.sleep(5)
        main_menu()


    clear()
    selection = 0
    while selection == 0:
        print(("-" * 15) + "MAIN MENU" + ("-" * 15) + "\n")
        print("1: Input a message and a corresponding time of delay before its display.")
        print("2: Print your customized list of messages.")
        print("3: Print random messages with random delays.\n")

        selection = int(input(
            "Please select one of the options, by typing in the corresponding number:"))

        if selection == 1:
            option_1()
        elif selection == 2:
            option_2()
        elif selection == 3:
            option_3()
        else:
            clear()
            print("Please select from options 1 - 3.\n")
            time.sleep(1.5)
            main_menu()

编辑(最终解决方案供将来引用):

感谢 Almog David 的建议，以下是我修改函数以使其按预期工作的方法。我希望这对将来寻找解决方案的人有所帮助。

选项_2():

 def option_2():
    global messages_and_times

    clear()
    threads = []
    print("Printing initialized:\n")

    def threading_function(message, seconds):
        time.sleep(seconds)
        print(message)

    for message, seconds in messages_and_times.items():
        t = Thread(target=threading_function, args=(message, seconds))
        t.start()
        threads.append(t)

    for t in threads:
        t.join()

    time.sleep(0.5)
    print(
        "\nPrinting is finished. You will be returned to the main menu in 5 seconds.")
    time.sleep(5)
    main_menu()

选项_3():

def option_3():
        clear()
        messages = ["message_1", "message_2", "message_3", "message_4", "message_5",
                    "message_6", "message_7", "message_8", "message_9", "message_10"]
        threads = []
        print("Printing initialized:\n")

        def threading_function(message, seconds):
            time.sleep(seconds)
            print(message)

        for message in messages:
            t = Thread(target=threading_function, args=(
                message, random.choice(range(1, 11))))
            t.start()
            threads.append(t)
        for t in threads:
            t.join()

        time.sleep(0.5)
        print(
            "\nPrinting is finished. You will be returned to the main menu in 5 seconds.")
        time.sleep(5)
        main_menu()

Answer 1

问题是您只等待最后一个线程加入(因为循环结束时“t”变量保存着最后创建的 Thread 对象)，因此当最后一个线程完成并且程序继续时，join 函数返回。

即使在选项 2 上，我也能够通过提供以下内容重现此错误:

messages_and_times = {"message_0": 3,
                  "message_1": 3,
                  "message_2": 1}

上述配置的结果是:

message_2

Printing is finished. You will be returned to the main menu in 5 seconds.
message_0
message_1

您应该采取的措施来修复它:

threads = []

for message, seconds in messages_and_times.items():
    t = Thread(target=threading_function, args=(message, seconds))
    t.start()
    threads.append(t)

for t in threads:
    t.join()