1 效能相關 在編寫爬蟲時，效能的消耗主要在IO請求中，當單程序單執行緒模式下請求URL時必然會引起等待，從而使得請求整體變慢。 1.1 同步執行

import requests

def fetch_async(url):
    response = requests.get(url)
    return response

url_list = ['http://www.github.com', 'http://www.bing.com']
for url in url_list:
    fetch_async(url)

1.2 多執行緒執行

from concurrent.futures import ThreadPoolExecutor import requests

def fetch_async(url):
    response = requests.get(url)
    return response

url_list = ['http://www.github.com', 'http://www.bing.com']
pool = ThreadPoolExecutor(5)
for url in url_list:
    pool.submit(fetch_async, url)
pool.shutdown(wait=True)


 

1.3 多執行緒+回撥函式執行

from concurrent.futures import ThreadPoolExecutor import requests

def fetch_async(url):
    response = requests.get(url)
    return response

def callback(future):
    print(future.result())

url_list = ['http://www.github.com', 'http://www.bing.com']
pool = ThreadPoolExecutor(5)
for url in url_list:
    v = pool.submit(fetch_async, url)
    v.add_done_callback(callback)
pool.shutdown(wait=True)
 

1.4 多程序執行

from concurrent.futures import ProcessPoolExecutor import requests

def fetch_async(url):
    response = requests.get(url)
    return response

url_list = ['http://www.github.com', 'http://www.bing.com']
pool = ProcessPoolExecutor(5)
for url in url_list:
    pool.submit(fetch_async, url)
pool.shutdown(wait=True)
 

1.5 多程序+回撥函式執行

from concurrent.futures import ProcessPoolExecutor import requests

def fetch_async(url):
    response = requests.get(url)
    return response

def callback(future):
    print(future.result())

url_list = ['http://www.github.com', 'http://www.bing.com']
pool = ProcessPoolExecutor(5)
for url in url_list:
    v = pool.submit(fetch_async, url)
    v.add_done_callback(callback)
pool.shutdown(wait=True)

通過上述程式碼均可以完成對請求效能的提高，對於多執行緒和多進行的缺點是在IO阻塞時會造成了執行緒和程序的浪費，所以非同步IO回事首選： 2 非同步IO 2.1 asyncio示例1

import asyncio

@asyncio.coroutine
def func1():
    print('before...func1......')
    yield from asyncio.sleep(5)
    print('end...func1......')

tasks = [func1(), func1()]
loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.gather(*tasks))
loop.close()

2.2 asyncio示例2

import asyncio

@asyncio.coroutine
def fetch_async(host, url='/'):
    print(host, url)
    reader, writer = yield from asyncio.open_connection(host, 80)

    request_header_content = """GET %s HTTP/1.0\r\nHost: %s\r\n\r\n""" % (url, host,)
    request_header_content = bytes(request_header_content, encoding='utf-8')

    writer.write(request_header_content)
    yield from writer.drain()
    text = yield from reader.read()
    print(host, url, text)
    writer.close()

tasks = [
    fetch_async('www.cnblogs.com', '/wupeiqi/'),
    fetch_async('dig.chouti.com', '/pic/show?nid=4073644713430508&lid=10273091')
]

loop = asyncio.get_event_loop()
results = loop.run_until_complete(asyncio.gather(*tasks))
loop.close()

2.3 asyncio + aiohttp

import aiohttp
import asyncio

@asyncio.coroutine
def fetch_async(url):
    print(url)
    response = yield from aiohttp.request('GET', url)
    # data = yield from response.read()
    # print(url, data)
    print(url, response)
    response.close()

tasks = [fetch_async('http://www.google.com/'), fetch_async('http://www.chouti.com/')]

event_loop = asyncio.get_event_loop()
results = event_loop.run_until_complete(asyncio.gather(*tasks))
event_loop.close()

2.4 asyncio + requests

import asyncio
import requests

@asyncio.coroutine
def fetch_async(func, *args):
    loop = asyncio.get_event_loop()
    future = loop.run_in_executor(None, func, *args)
    response = yield from future
    print(response.url, response.content)

tasks = [
    fetch_async(requests.get, 'http://www.cnblogs.com/wupeiqi/'),
    fetch_async(requests.get, 'http://dig.chouti.com/pic/show?nid=4073644713430508&lid=10273091')]

loop = asyncio.get_event_loop()
results = loop.run_until_complete(asyncio.gather(*tasks))
loop.close()

2.5 gevent + requests

import gevent
import requests
from gevent import monkey

monkey.patch_all()

def fetch_async(method, url, req_kwargs):
    print(method, url, req_kwargs)
    response = requests.request(method=method, url=url, **req_kwargs)
    print(response.url, response.content)

# ##### 傳送請求 #####
gevent.joinall([
    gevent.spawn(fetch_async, method='get', url='https://www.python.org/', req_kwargs={}),
    gevent.spawn(fetch_async, method='get', url='https://www.yahoo.com/', req_kwargs={}),
    gevent.spawn(fetch_async, method='get', url='https://github.com/', req_kwargs={}),
])

# ##### 傳送請求（協程池控制最大協程數量） #####
# from gevent.pool import Pool
# pool = Pool(None)
# gevent.joinall([
#     pool.spawn(fetch_async, method='get', url='https://www.python.org/', req_kwargs={}),
#     pool.spawn(fetch_async, method='get', url='https://www.yahoo.com/', req_kwargs={}),
#     pool.spawn(fetch_async, method='get', url='https://www.github.com/', req_kwargs={}),
# ])

2.6 grequests

import grequests

request_list = [
    grequests.get('http://httpbin.org/delay/1', timeout=0.001),
    grequests.get('http://fakedomain/'),
    grequests.get('http://httpbin.org/status/500')
]


# ##### 執行並獲取響應列表 #####
# response_list = grequests.map(request_list)
# print(response_list)


# ##### 執行並獲取響應列表（處理異常） #####
# def exception_handler(request, exception):
# print(request,exception)
#     print("Request failed")

# response_list = grequests.map(request_list, exception_handler=exception_handler)
# print(response_list)

2.7 Twisted示例

from twisted.web.client import getPage, defer
from twisted.internet import reactor

def all_done(arg):
    reactor.stop()

def callback(contents):
    print(contents)

deferred_list = []

url_list = ['http://www.bing.com', 'http://www.baidu.com', ]
for url in url_list:
    deferred = getPage(bytes(url, encoding='utf8'))
    deferred.addCallback(callback)
    deferred_list.append(deferred)

dlist = defer.DeferredList(deferred_list)
dlist.addBoth(all_done)
reactor.run()

2.8 Tornado

from tornado.httpclient import AsyncHTTPClient
from tornado.httpclient import HTTPRequest
from tornado import ioloop

def handle_response(response):
    """
    處理返回值內容（需要維護計數器，來停止IO迴圈），呼叫 ioloop.IOLoop.current().stop()
    :param response: 
    :return: 
    """
    if response.error:
        print("Error:", response.error)
    else:
        print(response.body)

def func():
    url_list = [
        'http://www.baidu.com',
        'http://www.bing.com',
    ]
    for url in url_list:
        print(url)
        http_client = AsyncHTTPClient()
        http_client.fetch(HTTPRequest(url), handle_response)
ioloop.IOLoop.current().add_callback(func)
ioloop.IOLoop.current().start()

2.9 Twisted更多

from twisted.internet import reactor
from twisted.web.client import getPage
import urllib.parse

def one_done(arg):
    print(arg)
    reactor.stop()

post_data = urllib.parse.urlencode({'check_data': 'adf'})
post_data = bytes(post_data, encoding='utf8')
headers = {b'Content-Type': b'application/x-www-form-urlencoded'}
response = getPage(bytes('http://dig.chouti.com/login', encoding='utf8'),
                   method=bytes('POST', encoding='utf8'),
                   postdata=post_data,
                   cookies={},
                   headers=headers)
response.addBoth(one_done)

reactor.run()

以上均是Python內建以及第三方模組提供非同步IO請求模組，使用簡便大大提高效率，而對於非同步IO請求的本質則是【非阻塞Socket】+【IO多路複用】：

史上最牛逼的非同步IO模組

import select
import socket
import time

class AsyncTimeoutException(TimeoutError):
    """
    請求超時異常類
    """

    def __init__(self, msg):
        self.msg = msg
        super(AsyncTimeoutException, self).__init__(msg)

class HttpContext(object):
    """封裝請求和相應的基本資料"""
    def __init__(self, sock, host, port, method, url, data, callback, timeout=5):
        """
        sock: 請求的客戶端socket物件
        host: 請求的主機名
        port: 請求的埠
        port: 請求的埠
        method: 請求方式
        url: 請求的URL
        data: 請求時請求體中的資料
        callback: 請求完成後的回撥函式
        timeout: 請求的超時時間
        """
        self.sock = sock
        self.callback = callback
        self.host = host
        self.port = port
        self.method = method
        self.url = url
        self.data = data
        self.timeout = timeout
        self.__start_time = time.time()
        self.__buffer = []

    def is_timeout(self):
        """當前請求是否已經超時"""
        current_time = time.time()
        if (self.__start_time + self.timeout) < current_time:
            return True

    def fileno(self):
        """請求sockect物件的檔案描述符，用於select監聽"""
        return self.sock.fileno()

    def write(self, data):
        """在buffer中寫入響應內容"""
        self.__buffer.append(data)

    def finish(self, exc=None):
        """在buffer中寫入響應內容完成，執行請求的回撥函式"""
        if not exc:
            response = b''.join(self.__buffer)
            self.callback(self, response, exc)
        else:
            self.callback(self, None, exc)

    def send_request_data(self):
        content = """%s %s HTTP/1.0\r\nHost: %s\r\n\r\n%s""" % (
            self.method.upper(), self.url, self.host, self.data,)
        return content.encode(encoding='utf8')

class AsyncRequest(object):
    def __init__(self):
        self.fds = []
        self.connections = []

    def add_request(self, host, port, method, url, data, callback, timeout):
        """建立一個要請求"""
        client = socket.socket()
        client.setblocking(False)
        try:
            client.connect((host, port))
        except BlockingIOError as e:
            pass
            # print('已經向遠端傳送連線的請求')
        req = HttpContext(client, host, port, method, url, data, callback, timeout)
        self.connections.append(req)
        self.fds.append(req)

    def check_conn_timeout(self):
        """檢查所有的請求，是否有已經連線超時，如果有則終止"""
        timeout_list = []
        for context in self.connections:
            if context.is_timeout():
                timeout_list.append(context)
        for context in timeout_list:
            context.finish(AsyncTimeoutException('請求超時'))
            self.fds.remove(context)
            self.connections.remove(context)

    def running(self):
        """事件迴圈，用於檢測請求的socket是否已經就緒，從而執行相關操作"""
        while True:
            r, w, e = select.select(self.fds, self.connections, self.fds, 0.05)
            if not self.fds:
                return
            for context in r:
                sock = context.sock
                while True:
                    try:
                        data = sock.recv(8096)
                        if not data:
                            self.fds.remove(context)
                            context.finish()
                            break
                        else:
                            context.write(data)
                    except BlockingIOError as e:
                        break
                    except TimeoutError as e:
                        self.fds.remove(context)
                        self.connections.remove(context)
                        context.finish(e)
                        break
            for context in w:
                # 已經連線成功遠端伺服器，開始向遠端傳送請求資料
                if context in self.fds:
                    data = context.send_request_data()
                    context.sock.sendall(data)
                    self.connections.remove(context)
            self.check_conn_timeout()

if __name__ == '__main__':
    def callback_func(context, response, ex):
        """
        :param context: HttpContext物件，內部封裝了請求相關資訊
        :param response: 請求響應內容
        :param ex: 是否出現異常（如果有異常則值為異常物件；否則值為None）
        :return:
        """
        print(context, response, ex)

    obj = AsyncRequest()
    url_list = [
        {'host': 'www.google.com', 'port': 80, 'method': 'GET', 'url': '/', 'data': '', 'timeout': 5,
         'callback': callback_func},
        {'host': 'www.baidu.com', 'port': 80, 'method': 'GET', 'url': '/', 'data': '', 'timeout': 5,
         'callback': callback_func},
        {'host': 'www.bing.com', 'port': 80, 'method': 'GET', 'url': '/', 'data': '', 'timeout': 5,
         'callback': callback_func},
    ]
    for item in url_list:
        print(item)
        obj.add_request(**item)

    obj.running()