在编写爬虫时，性能的消耗主要在IO请求中，当单进程单线程模式下请求URL时必然会引起等待，从而使得请求整体变慢。
1. 同步执行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)
2. 多线程执行（多个线程并发执行，时间长短取决于最长的URL请求）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)
3. 多进程执行（在CPU核心数足够的情况下，多个进程并行执行，时间长短取决于最长的URL请求，理论上会快于多线程）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)
4. 多线程+回调函数（实现了异步非阻塞，在IO等待的情况下可以做其它事情）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)
5. 多进程+回调函数（实现了异步非阻塞，在IO等待的情况下可以做其它事情）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)通过上述代码均可以完成对请求性能的提高，对于多线程和多进程的缺点是在IO阻塞时会造成了线程和进程的浪费，所以异步IO会是首选：
1. asyncio示例一
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. asyncio示例二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
Host: %s
""" % (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()
3. asyncio + aiohttpimport 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()
4. asyncio + requestsimport 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()
5. gevent + requestsimport 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)
# ##### 发送请求 #####
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={}),
])
# ##### 发送请求（协程池控制最大协程数量） #####
# 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={}),
# ])
6. grequests（封装的 gevent + requests）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')
]
# ##### 执行并获取响应列表 #####
# response_list = grequests.map(request_list)
# print(response_list)
# ##### 执行并获取响应列表（处理异常） #####
# def exception_handler(request, exception):
# print(request,exception)
# print("Request failed")
# response_list = grequests.map(request_list, exception_handler=exception_handler)
# print(response_list)
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()
8. Tornadofrom tornado.httpclient import AsyncHTTPClient
from tornado.httpclient import HTTPRequest
from tornado import ioloop
def handle_response(response):
"""
处理返回值内容（需要维护计数器，来停止IO循环），调用 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()
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内置以及第三方模块提供异步IO请求模块，使用简便大大提高效率，而对于异步IO请求的本质则是【非阻塞Socket】+【IO多路复用】： import select
import socket
import time
class AsyncTimeoutException(TimeoutError):
"""
请求超时异常类
"""
def __init__(self, msg):
self.msg = msg
super(AsyncTimeoutException, self).__init__(msg)
class HttpContext(object):
"""封装请求和相应的基本数据"""
def __init__(self, sock, host, port, method, url, data, callback, timeout=5):
"""
sock: 请求的客户端socket对象
host: 请求的主机名
port: 请求的端口
port: 请求的端口
method: 请求方式
url: 请求的URL
data: 请求时请求体中的数据
callback: 请求完成后的回调函数
timeout: 请求的超时时间
"""
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):
"""当前请求是否已经超时"""
current_time = time.time()
if (self.__start_time + self.timeout) < current_time:
return True
def fileno(self):
"""请求sockect对象的文件描述符，用于select监听"""
return self.sock.fileno()
def write(self, data):
"""在buffer中写入响应内容"""
self.__buffer.append(data)
def finish(self, exc=None):
"""在buffer中写入响应内容完成，执行请求的回调函数"""
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
Host: %s
%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):
"""创建一个要请求"""
client = socket.socket()
client.setblocking(False)
try:
client.connect((host, port))
except BlockingIOError as e:
pass
# print('已经向远程发送连接的请求')
req = HttpContext(client, host, port, method, url, data, callback, timeout)
self.connections.append(req)
self.fds.append(req)
def check_conn_timeout(self):
"""检查所有的请求，是否有已经连接超时，如果有则终止"""
timeout_list = []
for context in self.connections:
if context.is_timeout():
timeout_list.append(context)
for context in timeout_list:
context.finish(AsyncTimeoutException('请求超时'))
self.fds.remove(context)
self.connections.remove(context)
def running(self):
"""事件循环，用于检测请求的socket是否已经就绪，从而执行相关操作"""
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:
# 已经连接成功远程服务器，开始向远程发送请求数据
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对象，内部封装了请求相关信息
:param response: 请求响应内容
:param ex: 是否出现异常（如果有异常则值为异常对象；否则值为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()