asyncio是從pytohn3.4開始添加到標準庫中的一個強大的異步併發庫，能夠很好地解決python中高併發的問題，入門學習能夠參考官方文檔html
併發訪問能極大的提升爬蟲的性能，可是requests訪問網頁是阻塞的，沒法併發，因此咱們須要一個更牛逼的庫 aiohttp ，它的用法與requests類似，能夠當作是異步版的requests，下面經過實戰爬取貓眼電影專業版來熟悉它們的使用：python
1. 分析
分析網頁源代碼發現貓眼專業版是一個動態網頁，其中的數據都是後臺傳送的，打開F12調試工具，再刷新網頁選擇XHR後發現第一條就是後臺發來的電影數據，由此獲得接口 https://box.maoyan.com/promovie/api/box/second.json?beginDate=日期json
在這裏插入圖片描述
2. 異步爬取
建立20個任務來併發爬取20天的電影信息並寫入csv文件，同時計算一下耗費的時間api
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import asyncio
from
aiohttp import ClientSession
import aiohttp
import time
import csv
import ssl
ssl._create_default_https_context = ssl._create_unverified_context
headers = {
'User-Agent'
:
'Mozilla/5.0 (Windows NT 10.0; Win64; x64) '
'AppleWebKit/537.36 (KHTML, like Gecko) '
'Chrome/67.0.3396.99 Safari/537.36'
}
# 協程函數，完成一個無阻塞的任務
async def get_one_page(url):
try
:
conn = aiohttp.TCPConnector(verify_ssl=False) # 防止ssl報錯
async with aiohttp.ClientSession(connector=conn)
as
session: # 建立session
async with session.
get
(url, headers=headers)
as
r:
# 返回解析爲字典的電影數據
return
await r.json()
except Exception
as
e:
print(
'請求異常： '
+ str(e))
return
{}
# 解析函數，提取每一條內容並寫入csv文件
def parse_one_page(movie_dict, writer):
try
:
movie_list = movie_dict[
'data'
][
'list'
]
for
movie
in
movie_list:
movie_name = movie[
'movieName'
]
release = movie[
'releaseInfo'
]
sum_box = movie[
'sumBoxInfo'
]
box_info = movie[
'boxInfo'
]
box_rate = movie[
'boxRate'
]
show_info = movie[
'showInfo'
]
show_rate = movie[
'showRate'
]
avg_show_view = movie[
'avgShowView'
]
avg_seat_view = movie[
'avgSeatView'
]
writer.writerow([movie_name, release, sum_box, box_info, box_rate,
show_info, show_rate, avg_show_view, avg_seat_view])
return
(
'寫入成功'
)
except Exception
as
e:
return
(
'解析異常： '
+ str(e))
# 併發爬取
async def main():
# 待訪問的20個URL連接
urls = [
'https://box.maoyan.com/promovie/api/box/second.json?beginDate=201904{}{}'
.format(i, j)
for
i
in
range(1, 3)
for
j
in
range(10)]
# 任務列表
tasks = [get_one_page(url)
for
url
in
urls]
# 併發執行並保存每個任務的返回結果
results = await asyncio.gather(*tasks)
# 處理每個結果
with open(
'pro_info.csv'
,
'w'
)
as
f:
writer = csv.writer(f)
for
result
in
results:
print(parse_one_page(result, writer))
if
__name__ ==
"__main__"
:
start = time.time()
# asyncio.run(main())
# python3.7以前的寫法
loop = asyncio.get_event_loop()
loop.run_until_complete(main())
loop.close()
print(time.time()-start)
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3. 對比同步爬取
import requests import csv import time headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) ' 'AppleWebKit/537.36 (KHTML, like Gecko) ' 'Chrome/67.0.3396.99 Safari/537.36'} def get_one_page(url): try: r = requests.get(url, headers=headers) r.raise_for_status() r.encoding = r.apparent_encoding return r.json() except Exception as e: print('請求異常： ' + e) return {} def parse_one_page(movie_dict, writer): try: movie_list = movie_dict['data']['list'] for movie in movie_list: movie_name = movie['movieName'] release = movie['releaseInfo'] sum_box = movie['sumBoxInfo'] box_info = movie['boxInfo'] box_rate = movie['boxRate'] show_info = movie['showInfo'] show_rate = movie['showRate'] avg_show_view = movie['avgShowView'] avg_seat_view = movie['avgSeatView'] writer.writerow([movie_name, release, sum_box, box_info, box_rate, show_info, show_rate, avg_show_view, avg_seat_view]) print('寫入成功') except Exception as e: print('解析異常： ' + e) def main(): # 待訪問的20個URL連接 urls = ['https://box.maoyan.com/promovie/api/box/second.json?beginDate=201903{}{}'.format(i, j) for i in range(1, 3) for j in range(10)] with open('out/pro_info.csv', 'w') as f: writer = csv.writer(f) for url in urls: # 逐一處理 movie_dict = get_one_page(url) parse_one_page(movie_dict, writer) if __name__ == '__main__': a = time.time() main() print(time.time() - a)
在這裏插入圖片描述
能夠看到使用asyncio+aiohttp的異步爬取方式要比簡單的requests同步爬取快上很多，尤爲是爬取大量網頁的時候，這種差距會很是明顯。session