为什么并发。与futures一起使用时,futures executor map抛出错误。所有期货交易完成后,as\U完成了吗?

我正在尝试同时发送HTTP请求。为此,我使用 concurrent.futures

下面是简单的代码:

import requests
from concurrent import futures

data = range(10)


def send_request(item):
    requests.get("https://httpbin.org/ip")
    print("Request {} complete.".format(item))


executor = futures.ThreadPoolExecutor(max_workers=25)

futures_ = executor.map(send_request, data)

for f in futures.as_completed(futures_):
    f.result()

如果我运行它,我可以看到请求是异步发送的,这正是我想要做的。但是,当所有请求都完成时,我得到以下错误:

Request 0 complete.
Request 6 complete.
...
Request 7 complete.
Request 9 complete.
Request 3 complete.
Traceback (most recent call last):
  File "send_thread.py", line 18, in <module>
    for f in futures.as_completed(futures_):
  File "/usr/local/Cellar/python3/3.6.4/Frameworks/Python.framework/Versions/3.6/lib/python3.6/concurrent/futures/_base.py", line 219, in as_completed
    with _AcquireFutures(fs):
  File "/usr/local/Cellar/python3/3.6.4/Frameworks/Python.framework/Versions/3.6/lib/python3.6/concurrent/futures/_base.py", line 146, in __enter__
    future._condition.acquire()
AttributeError: 'NoneType' object has no attribute '_condition'

这是一个很奇怪的错误。在这里 executor.map 似乎有问题。如果我用下面的行替换map,它将按预期工作。

futures_ = [executor.submit(send_request, x) for x in data]

我错过了什么?试图找出两者之间的区别,但似乎无法理解上述问题的原因。如有任何意见,我们将不胜感激。