Python Multiprocessing Lib Error (AttributeError: __exit__)

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:

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().

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

or create your own terminating() context manager:

from contextlib import contextmanager@contextmanagerdef terminating(thing):    try:        yield thing    finally:        thing.terminate()with terminating(Pool(processes=2)) as pool:    pool.map(myFunction, mylist)    pool.map(myfunction2, mylist2)

with statement is for object that have __enter__ and __exit__ functions, i.e. Context Manager Types
multiprocessing.Pool is not Context Manager Type.try do the following:

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