8

我正在使用 asyncio 模块进行测试，但是我需要提示/建议如何以异步方式获取大型电子邮件。

我有一个包含邮件帐户用户名和密码的列表。

data = [
    {'usern': 'foo@bar.de', 'passw': 'x'},
    {'usern': 'foo2@bar.de', 'passw': 'y'},
    {'usern': 'foo3@bar.de', 'passw': 'z'} (...)
]

我想过：

loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.wait([get_attachment(d) for d in data]))
loop.close()

但是，较长的部分是下载电子邮件附件。

电子邮件：

@asyncio.coroutine
def get_attachment(d):
    username = d['usern']
    password = d['passw']

    connection = imaplib.IMAP4_SSL('imap.bar.de')
    connection.login(username, password)
    connection.select()

    # list all available mails
    typ, data = connection.search(None, 'ALL')

    for num in data[0].split():
        # fetching each mail
        typ, data = connection.fetch(num, '(RFC822)')
        raw_string = data[0][1].decode('utf-8')
        msg = email.message_from_string(raw_string)
        for part in msg.walk():
            if part.get_content_maintype() == 'multipart':
                continue

            if part.get('Content-Disposition') is None:
                continue

            if part.get_filename():
                body = part.get_payload(decode=True)
                # do something with the body, async?

    connection.close()
    connection.logout()

如何以异步方式处理所有（下载附件）邮件？

4

2 回答 2

7

如果您没有基于异步 I/O 的 imap 库，则可以只使用 aconcurrent.futures.ThreadPoolExecutor在线程中执行 I/O。Python 将在 I/O 期间释放 GIL，因此您将获得真正的并发：

def init_connection(d):    
    username = d['usern']
    password = d['passw']

    connection = imaplib.IMAP4_SSL('imap.bar.de')
    connection.login(username, password)
    connection.select()
    return connection

local = threading.local() # We use this to get a different connection per thread
def do_fetch(num, d, rfc):
    try:
        connection = local.connection
    except AttributeError:
        connnection = local.connection = init_connection(d)
    return connnection.fetch(num, rfc)

@asyncio.coroutine
def get_attachment(d, pool):
    connection = init_connection(d)    
    # list all available mails
    typ, data = connection.search(None, 'ALL')

    # Kick off asynchronous tasks for all the fetches
    loop = asyncio.get_event_loop()
    futs = [asyncio.create_task(loop.run_in_executor(pool, do_fetch, num, d, '(RFC822)'))
                for num in data[0].split()]

    # Process each fetch as it completes
    for fut in asyncio.as_completed(futs):
        typ, data = yield from fut
        raw_string = data[0][1].decode('utf-8')
        msg = email.message_from_string(raw_string)
        for part in msg.walk():
            if part.get_content_maintype() == 'multipart':
                continue

            if part.get('Content-Disposition') is None:
                continue

            if part.get_filename():
                body = part.get_payload(decode=True)
                # do something with the body, async?

    connection.close()
    connection.logout()    


loop = asyncio.get_event_loop()
pool = ThreadPoolExecutor(max_workers=5)  # You can probably increase max_workers, because the threads are almost exclusively doing I/O.
loop.run_until_complete(asyncio.wait([get_attachment(d, pool) for d in data]))
loop.close()

这不如真正基于异步 I/O 的解决方案好，因为您仍然需要创建线程的开销，这会限制可伸缩性并增加额外的内存开销。由于所有代码都封装了实际的 I/O 调用，因此您也确实会降低GIL 速度。不过，如果您处理的邮件少于数千封，它应该仍然可以正常运行。

我们run_in_executor将ThreadPoolExecutor用作 asyncio 事件循环的一部分，将asyncio.async返回的协程对象包装在 aasyncio.Future中，并as_completed按照完成的顺序遍历 future。

编辑：

它似乎imaplib不是线程安全的。我已经通过 编辑了我的答案以使用线程本地存储threading.local，它允许我们为每个线程创建一个连接对象，它可以在线程的整个生命周期中重复使用（这意味着您num_workers只创建连接对象，而不是每个fetch) 的新连接。

于 2014-07-30T14:19:23.957 回答
5

我有同样的需求：使用完全异步的 python 3 获取电子邮件。如果这里的其他人感兴趣，我在这里推送了一个 asyncio IMAP 库：https ://github.com/bamthomas/aioimaplib

你可以像这样使用它：

import asyncio
from aioimaplib import aioimaplib

@asyncio.coroutine
def wait_for_new_message(host, user, password):
    imap_client = aioimaplib.IMAP4(host=host)
    yield from imap_client.wait_hello_from_server()

    yield from imap_client.login(user, password)
    yield from imap_client.select()

    asyncio.async(imap_client.idle())
    id = 0
    while True:
        msg = yield from imap_client.wait_server_push()
        print('--> received from server: %s' % msg)
        if 'EXISTS' in msg:
            id = msg.split()[0]
            imap_client.idle_done()
            break

    result, data = yield from imap_client.fetch(id, '(RFC822)')
    email_message = email.message_from_bytes(data[0])

    attachments = []
    body = ''
    for part in email_message.walk():
        if part.get_content_maintype() == 'multipart':
            continue
        if part.get_content_maintype() == 'text' and 'attachment' not in part.get('Content-Disposition', ''):
            body = part.get_payload(decode=True).decode(part.get_param('charset', 'ascii')).strip()
        else:
            attachments.append(
                {'type': part.get_content_type(), 'filename': part.get_filename(), 'size': len(part.as_bytes())})

    print('attachments : %s' % attachments)
    print('body : %s' % body)
    yield from imap_client.logout()



if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(wait_for_new_message('my.imap.server', 'user', 'pass'))

带有附件的大型电子邮件也可以使用 asyncio 下载。

于 2016-07-05T14:44:50.757 回答