2019独角兽企业重金招聘Python工程师标准>>> 
concurrent.futures模块提供了一个异步执行callables的高级接口。 可以使用ThreadPoolExecutor和ProcessPoolExecutor。 两者都继承了相同的接口，该接口由抽象的Executor类定义。
一个抽象类，提供异步执行调用的方法。 它不应该直接使用，而是通过其具体的子类。
submit (fn, *args, **kwargs)：提交执行的函数并获取一个Future对象，例如：
with ThreadPoolExecutor(max_workers=1) as executor:future = executor.submit(pow, 323, 1235)print(future.result())
ThreadPoolExecutor：是Executor子类，它使用一个线程池来异步执行调用。concurrent.futures.ThreadPoolExecutor(max_workers=None, thread_name_prefix='', initializer=None, initargs=())。例如：
import concurrent.futures import urllib.request
URLS = ['http://www.foxnews.com/','http://www.cnn.com/','http://europe.wsj.com/','http://www.bbc.co.uk/','http://some-made-up-domain.com/']# Retrieve a single page and report the URL and contents
def load_url(url, timeout):with urllib.request.urlopen(url, timeout=timeout) as conn:return conn.read()# We can use a with statement to ensure threads are cleaned up promptly
with concurrent.futures.ThreadPoolExecutor(max_workers=5) as executor:# Start the load operations and mark each future with its URLfuture_to_url = {executor.submit(load_url, url, 60): url for url in URLS}for future in concurrent.futures.as_completed(future_to_url):url = future_to_url[future]try:data = future.result()except Exception as exc:print('%r generated an exception: %s' % (url, exc))else:print('%r page is %d bytes' % (url, len(data))) ProcessPoolExecutor：concurrent.futures.ProcessPoolExecutor(max_workers=None, mp_context=None, initializer=None, initargs=())：使用如下：
import concurrent.futures import math
executor = ProcessPoolExecutor(max_workers=5)def is_prime(n):if n % 2 == 0:return Falsesqrt_n = int(math.floor(math.sqrt(n)))for i in range(3, sqrt_n + 1, 2):if n % i == 0:return Falsereturn Truedef main():for i in range(10):
future = executor.submit(is_prime, n)if __name__ == '__main__':main()
Future: Future类封装了可调用的异步执行。 该实例由Executor.submit（）创建。
