multiprocessing.dummy why AttributeError: 'module' object has no attribute 'dummy'

Question

我在Python遇到了一件奇怪的事：

>>> import multiprocessing

>>> thread_pool = multiprocessing.dummy.Pool()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'dummy'

但是，当我尝试以下操作时：

>>> from multiprocessing.dummy import Pool as ThreadPool
>>> ThreadPool()
<multiprocessing.pool.ThreadPool object at 0x7faf9308d4a8>

和

>>> import multiprocessing.dummy
>>> multiprocessing.dummy.Pool()
<multiprocessing.pool.ThreadPool object at 0x7faf9308d2e8>

一切正常。我知道 import xxx 和 from xxx import 之间的区别，我想知道为什么它会引发 AttributeError。 我的问题是为什么我不能在 import multiprocessing 之后使用 multiprocessing.dummy?

Answer 1

multiprocessing.dummy 包未在 multiprocessing.__init__.py 中导入。因此，

>>> import multiprocessing

>>> thread_pool = multiprocessing.dummy.Pool()

不起作用。形成文档字符串：

# This package is intended to duplicate the functionality (and much of
# the API) of threading.py but uses processes instead of threads.  A
# subpackage 'multiprocessing.dummy' has the same API but is a simple
# wrapper for 'threading'.

我猜这个子包是故意隐藏以防止人们不小心使用它。

multiprocessing.dummy why AttributeError: 'module' object has no attribute 'dummy'

multiprocessing.dummy why AttributeError: 'module' object has no attribute 'dummy'

python

module

multiprocessing

python-import