使用Python 2.7/Windows运行多处理作业 [英] Run a multiprocessing job with Python 2.7 / Windows

问题描述

基于此答案，我想在Python 2.7/Windows上运行此multiprocessing作业:

Based on this answer, I'd like to run this multiprocessing job with Python 2.7 / Windows:

def main():
    import itertools as it
    from multiprocessing import Pool

    def dothejob(i, j, k):
        print i, j, k

    the_args = it.product(range(100), range(100), range(100))
    pool = Pool(4)

    def jobWrapper(args): 
        return dothejob(*args)

    res = pool.map(jobWrapper, the_args)

if __name__ == '__main__':
    main()    

main()和最后两行是必需的，因为如果没有它们，则存在一个众所周知的错误:

The main() and the last two lines are necessary because without them, there's the well known bug:

这可能意味着您在Windows上并且拥有 忘记在主模块中使用适当的习惯用法:

This probably means that you are on Windows and you have forgotten to use the proper idiom in the main module:

if __name__ == '__main__':
    ....

但是即使如此，我仍然收到此错误:

But even with that, I get this error:

文件"C:\ Users \ User \ Desktop \ test.py"，主行中的第14行 res = pool.map(jobWrapper，the_args) 地图中的文件"C:\ Python27 \ lib \ multiprocessing \ pool.py"，第251行 返回self.map_async(func，可迭代，块大小).get() 在get中的文件"C:\ Python27 \ lib \ multiprocessing \ pool.py"，行558 提高自我价值 cPickle.PicklingError:无法腌制:属性查找> 内置.功能失败

File "C:\Users\User\Desktop\test.py", line 14, in main res = pool.map(jobWrapper, the_args) File "C:\Python27\lib\multiprocessing\pool.py", line 251, in map return self.map_async(func, iterable, chunksize).get() File "C:\Python27\lib\multiprocessing\pool.py", line 558, in get raise self._value cPickle.PicklingError: Can't pickle : attribute lookup >builtin.function failed

此处涉及cPickle的位置，以及此错误的原因/解决方法?

Where is there a cPickle involved here and why this error / how to solve it?

推荐答案

所有定义都必须在模块范围内:

All definitions must be on module scope:

import itertools as it
from multiprocessing import Pool, freeze_support

def dothejob(i, j, k):
    print i, j, k

def jobWrapper(args): 
    return dothejob(*args)

def main():
    the_args = it.product(range(100), range(100), range(100))
    pool = Pool(4)
    res = pool.map(jobWrapper, the_args)

if __name__ == '__main__':
    freeze_support() #you need this in windows
    main()

您还需要在Windows中进行freeze_support调用

You also need freeze_support call in windows

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