It's only in imap, in map it's ok. The following code explains the issue:


from multiprocessing.pool import ThreadPool

pool = ThreadPool(10)

def gen():
    yield 1 + '1' # here is an error

try:
    next((pool.imap(str, gen())))
except:
    # Will be catched using pool.map normally, but using pool.imap will be not.
    # Instead it hangs. This is the same for ThreadPool and Pool.
    print('this will not be printed because thread is hanging')