Python 给出 AttributeError 的多处理示例
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Multiprocessing example giving AttributeError
提问by PiccolMan
I am trying to implement multiprocessing in my code, and so, I thought that I would start my learning with some examples. I used the first example found in this documentation.
我试图在我的代码中实现多处理，因此，我想我会从一些例子开始我的学习。我使用了本文档中的第一个示例。
from multiprocessing import Pool
def f(x):
return x*x
if __name__ == '__main__':
with Pool(5) as p:
print(p.map(f, [1, 2, 3]))
When I run the above code I get an AttributeError: can't get attribute 'f' on <module '__main__' (built-in)>. I do not know why I am getting this error. I am also using Python 3.5 if that helps.
当我运行上面的代码时，我得到一个AttributeError: can't get attribute 'f' on <module '__main__' (built-in)>. 我不知道为什么会收到此错误。如果有帮助，我也在使用 Python 3.5。
回答by hr87
This problem seems to be a design feature of multiprocessing.Pool. See https://bugs.python.org/issue25053. For some reason Pool does not always work with objects not defined in an imported module. So you have to write your function into a different file and import the module.
这个问题似乎是 multiprocessing.Pool 的一个设计特性。请参阅https://bugs.python.org/issue25053。出于某种原因，Pool 并不总是与未在导入模块中定义的对象一起使用。因此，您必须将函数写入不同的文件并导入模块。
File: defs.py
文件：defs.py
def f(x):
return x*x
File: run.py
文件：run.py
from multiprocessing import Pool
import defs
if __name__ == '__main__':
with Pool(5) as p:
print(p.map(defs.f, [1, 2, 3]))
If you use print or a different built-in function, the example should work. If this is not a bug (according to the link), the given example is chosen badly.
如果您使用 print 或不同的内置函数，该示例应该可以工作。如果这不是错误（根据链接），则给定的示例选择不当。
