Python多进程代码输出符合预期但报NameError：fib_position未定义

使用多进程生成指定数量文件并写入斐波那契数时，明明已定义fib_position变量，却触发NameError提示未定义。代码及错误信息如下：

代码 #

def create_folder():
        path="C:\Users\HansPeterJonasHogh-J\dev\docs\pyhtonexercise\async_multi"
        os.chdir(path)
        fib_folder= 'fibFolder-01'
        os.makedirs(fib_folder)

def generate_array(fib_position):
    fibarray=[1,] 
    num1 = 0
    num2 = 1
    current_index = 1
    fibnum=0
    while current_index < fib_position:
            fibnum = (num1+num2)
            num1 = num2
            num2 = fibnum
            current_index = (current_index+1)
            fibarray.append(int(fibnum))
    return(fibarray)

def write_file(fibarray):
    for X in range(1, len(fibarray) +1):
        with open(f"fib-number-{X}.txt", "w") as file:
            file.write(str(fibarray[:X]))
            file.close()

if __name__== "__main__":
    fib_position = 7


# multiprocessing
st = time.time()

p2 = multiprocessing.Process(target=generate_array, args=(fib_position, ))


create_folder()
p2.start()

#p1.join()
#p2.join()

st = time.time()
en = time.time()
print("time taken = ", en-st)

错误信息 #

J\dev\docs\pyhtonexercise\async_multi\three_programs.py", line 37, in <module>
    p2 = multiprocessing.Process(target=generate_array, args=(fib_position, ))
NameError: name 'fib_position' is not defined

fib_position变量定义在if __name__ == "__main__":代码块内部，而创建多进程的代码写在了该代码块的外部。

Python中，if __name__ == "__main__":是一个局部作用域代码块，内部定义的变量仅在该块内有效，外部代码无法直接访问。同时，启动多进程时子进程会重新导入脚本，顶层代码会被执行，但if __name__ == "__main__":内的代码不会在子进程中运行，双重因素导致变量无法被正确识别。

将所有和多进程相关的代码移到if __name__ == "__main__":代码块内部，同时补充缺失的导入语句、修复潜在的文件路径问题：

import os
import time
import multiprocessing

def create_folder():
        path="C:\Users\HansPeterJonasHogh-J\dev\docs\pyhtonexercise\async_multi"
        os.chdir(path)
        fib_folder= 'fibFolder-01'
        # 避免文件夹已存在触发报错
        if not os.path.exists(fib_folder):
            os.makedirs(fib_folder)
        # 切换到目标文件夹，确保文件生成在指定目录
        os.chdir(fib_folder)

def generate_array(fib_position):
    fibarray=[1,] 
    num1 = 0
    num2 = 1
    current_index = 1
    fibnum=0
    while current_index < fib_position:
            fibnum = (num1+num2)
            num1 = num2
            num2 = fibnum
            current_index = (current_index+1)
            fibarray.append(int(fibnum))
    return(fibarray)

def write_file(fibarray):
    for X in range(1, len(fibarray) +1):
        with open(f"fib-number-{X}.txt", "w") as file:
            file.write(str(fibarray[:X]))
            # with上下文管理器会自动关闭文件，无需手动调用close()

if __name__== "__main__":
    fib_position = 7

    # 多进程逻辑
    st = time.time()

    p2 = multiprocessing.Process(target=generate_array, args=(fib_position, ))

    create_folder()
    p2.start()
    p2.join()  # 等待子进程执行完成，避免主进程提前结束导致计时不准

    en = time.time()
    print("time taken = ", en-st)

额外优化说明：

• 补充了os、time、multiprocessing的导入语句（原代码缺失会触发其他报错）
• 增加文件夹存在判断，避免重复创建报错
• 切换到目标文件夹，确保文件生成在指定目录
• 移除手动file.close()，利用with语句自动管理文件资源
• 添加p2.join()，确保主进程等待子进程执行完毕再计算耗时

内容的提问来源于stack exchange，提问作者JnooriRS