問題描述

使用 pool.map(funct, iterable) 時出現此錯誤:

Am getting this error when using the pool.map(funct, iterable):

AttributeError: __exit__

沒有解釋，只是堆棧跟蹤到模塊內的 pool.py 文件.

No Explanation, only stack trace to the pool.py file within the module.

這樣使用:

with Pool(processes=2) as pool:
   pool.map(myFunction, mylist)
   pool.map(myfunction2, mylist2)

我懷疑picklability可能存在問題(python需要pickle，或將列表數據轉換為字節流)但我不確定這是真的還是如何調試.

I suspect there could be a problem with the picklability (python needs to pickle, or transform list data into byte stream) yet I'm not sure if this is true or if it is how to debug.

產生此錯誤的新代碼格式:

new format of code that produces this error :

def governingFunct(list):
    #some tasks
    def myFunction():
         # function contents
    with closing(Pool(processes=2)) as pool:
         pool.map(myFunction, sublist)
         pool.map(myFunction2, sublist2)

產生錯誤:

PicklingError: Can't pickle <type 'function'>: attribute lookup __builtin__.function failed

推薦答案

在 Python 2.x 和 3.0、3.1 和 3.2 中，multiprocessing.Pool() 對象不是上下文管理器.您不能在 with 語句中使用它們.只有在 Python 3.3 及更高版本中，您才能使用它們.來自 Python 3 multiprocessing.Pool() 文檔:

In Python 2.x and 3.0, 3.1 and 3.2, multiprocessing.Pool() objects are not context managers. You cannot use them in a with statement. Only in Python 3.3 and up can you use them as such. From the Python 3 multiprocessing.Pool() documentation:

3.3 版中的新功能:池對象現在支持上下文管理協議 - 請參閱上下文管理器類型.__enter__() 返回池對象，__exit__() 調用 terminate().

New in version 3.3: Pool objects now support the context management protocol – see Context Manager Types. __enter__() returns the pool object, and __exit__() calls terminate().

對于早期的 Python 版本，您可以使用 contextlib.closing()，但考慮到這將調用 pool.close()，而不是 pool.terminate().在這種情況下手動終止:

For earlier Python versions, you could use contextlib.closing(), but take into account this'll call pool.close(), not pool.terminate(). Terminate manually in that case:

from contextlib import closing

with closing(Pool(processes=2)) as pool:
    pool.map(myFunction, mylist)
    pool.map(myfunction2, mylist2)
    pool.terminate()

或創建自己的 terminating() 上下文管理器:

or create your own terminating() context manager:

from contextlib import contextmanager

@contextmanager
def terminating(thing):
    try:
        yield thing
    finally:
        thing.terminate()

with terminating(Pool(processes=2)) as pool:
    pool.map(myFunction, mylist)
    pool.map(myfunction2, mylist2)

這篇關于Python 多處理庫錯誤(AttributeError:__exit__)的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！