Python 3.4中的多处理是否已损坏？

Question

我正在尝试在Python 3中使用多处理模块.但是,每次我尝试设置池时,都会得到以下回溯.

Traceback (most recent call last):
  File "testmp.py", line 7, in <module>
    with Pool(5) as p:
  File "/usr/lib/python3.4/multiprocessing/context.py", line 118, in Pool
    context=self.get_context())
  File "/usr/lib/python3.4/multiprocessing/pool.py", line 150, in __init__
    self._setup_queues()
  File "/usr/lib/python3.4/multiprocessing/pool.py", line 243, in _setup_queues
    self._inqueue = self._ctx.SimpleQueue()
  File "/usr/lib/python3.4/multiprocessing/context.py", line 110, in SimpleQueue
    from .queues import SimpleQueue
  File "/usr/lib/python3.4/multiprocessing/queues.py", line 20, in <module>
    from queue import Empty, Full
ImportError: cannot import name 'Empty'

可以轻松触发此操作的最简单代码是多处理模块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]))

(来源:https://docs.python.org/3.4/library/multiprocessing.html)

我的问题:这是Python 3.4中的错误吗？或者我做错了什么？等效代码适用于Python 2.7.

Answer 1

你有一个名为的本地模块queue; 它会干扰标准库模块.

删除它或重命名它,你的代码将再次工作:

stackoverflow-3.4 mj$ cat test.py 
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]))

stackoverflow-3.4 mj$ touch queue.py
stackoverflow-3.4 mj$ bin/python test.py 
Traceback (most recent call last):
  File "test.py", line 7, in <module>
    with Pool(5) as p:
  File "/.../python3.4/multiprocessing/context.py", line 118, in Pool
    context=self.get_context())
  File "/.../python3.4/multiprocessing/pool.py", line 150, in __init__
    self._setup_queues()
  File "/.../python3.4/multiprocessing/pool.py", line 243, in _setup_queues
    self._inqueue = self._ctx.SimpleQueue()
  File "/.../lib/python3.4/multiprocessing/context.py", line 110, in SimpleQueue
    from .queues import SimpleQueue
  File "/.../lib/python3.4/multiprocessing/queues.py", line 20, in <module>
    from queue import Empty, Full
ImportError: cannot import name 'Empty'
stackoverflow-3.4 mj$ rm queue.py
stackoverflow-3.4 mj$ bin/python test.py 
[1, 4, 9]

如果您无法找到它,请运行python3 -c 'import queue; print(queue.__file__)'.