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From the error message you've shared, it seems that your Python program is encountering a common issue when using the multiprocessing module. This error typically occurs because Python's multiprocessing module needs to ensure that the main module can be safely imported by a new child process. Here is how to resolve this error:

The Problem

When a new process is started using Python's multiprocessing module, Python will try to import the main module. If the main module contains code that is not guarded by if __name__ == '__main__':, it will be executed again in each child process. This can lead to unintended behaviors or runtime errors if the entire script is not designed to be safe for importing, like what you're seeing.

• guarded: 被保护的

Solution

To fix this, you should encapsulate the entry point of your program or the part that triggers the creation of new processes within a block that checks if the script is being run as the main module. Here's how to do it:

• Encapsulate: 封装
• trigger: 触发

import multiprocessing

def worker():
    print("Worker function")

def main():
    # Create a multiprocessing pool or start new processes
    with multiprocessing.Pool(5) as pool:
        results = pool.apply_async(worker)
        # Get results, handle processes, etc.

if __name__ == '__main__':
    # This block ensures the contained code only runs in the main process
    multiprocessing.freeze_support()  # For Windows support when script is frozen
    main()

Explanation

1. if __name__ == '__main__':: This line checks if the script is being run directly (not imported). When a Python script is imported as a module, __name__ is set to the module's name. When executed directly, it is set to '__main__'.

2. multiprocessing.freeze_support(): This function is necessary for scripts that are going to be frozen into a standalone executable, especially on Windows. It can be omitted if you are not freezing the program but including it doesn’t harm.

3. Encapsulating the multiprocessing code: By placing the multiprocessing code inside a function called from within the if __name__ == '__main__': block, you prevent unintended execution of process-creation code when modules are imported.

By restructuring your program in this manner, you ensure that the multiprocessing initialization only occurs in the main environment, protecting against the execution in child processes that lead to the error you're encountering.

• against: 介词，用来表示“保护免受”或“防止”。用法是指通过某种方式来阻止或防范不希望发生的事情。

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