python网页爬虫开发之四-串行爬虫代码示例

实现功能：代理、限速、深度、反爬

import re

import queue

import urllib.parse

import urllib.robotparser

import time

from urllib import request

from datetime import datetime

def download(url, user_agent="wsap", num=2):

print("Downloading:"+url)

try:

req = request.Request(url)

req.add_header('user_agent', user_agent)

html = request.urlopen(req).read()

except Exception as e:

print('Download error:')

html = None

if num > 0:

if hasattr(e, "code") and 500 <= e.code < 600:

return download(url, user_agent, num-1)

return html

def link_crawler(seed_url, link_regex=None, delay=5, max_depth=-1, max_urls=-1, headers=None, user_agent='BadCrawler', proxy=None, num_retries=1):

crawl_queue = queue.deque([seed_url])

seen = {seed_url: 0}

num_urls = 0

rp = get_robots(seed_url)

throttle = Throttle(delay)

headers = headers or {}

if user_agent:

headers['User-agent'] = user_agent

while crawl_queue:

url = crawl_queue.pop()

if rp.can_fetch(user_agent, url):

throttle.wait(url)

html = download(url)

links = []

depth = seen[url]

if depth != max_depth:

if link_regex:

links.extend(link for link in get_links(html) if re.match(link_regex, link))

for link in links:

link = normalize(seed_url, link)

if link not in seen:

seen[link] = depth +1

if same_domain(seed_url, link):

crawl_queue.append(link)

num_urls += 1

if num_urls == max_urls:

break

else:

print('Blocked by robots.txt:'+url)

class Throttle:

def __init__(self, delay):

self.delay = delay

self.domains = {}

def wait(self, url):

domain = urllib.parse.urlparse(url).netloc

last_accessed = self.domains.get(domain)

if self.delay > 0 and last_accessed is not None:

sleep_secs = self.delay - (datetime.now() - last_accessed).seconds

if sleep_secs > 0:

time.sleep(sleep_secs)

self.domains[domain] = datetime.now()

def normalize(seed_url,link):

link, _ = urllib.parse.urldefrag(link)

return urllib.parse.urljoin(seed_url, link)

def same_domain(url1, url2):

return urllib.parse.urlparse(url1).netloc == urllib.parse.urlparse(url2).netloc

def get_robots(url):

rp = urllib.robotparser.RobotFileParser()

rp.set_url(urllib.parse.urljoin(url, '/robots.txt'))

rp.read()

return rp

def get_links(html):

webpage_regex = re.compile('<a[^>]+href=["\'](.*?)["\']', re.IGNORECASE)

html = html.decode('utf-8')

return webpage_regex.findall(html)

if __name__ == '__main__':

link_crawler('http://example.webscraping.com', '/places/default/view/', delay=0, num_retries=1, max_depth=1, user_agent='GoodCrawler')

巴特西

python网页爬虫开发之四-串行爬虫代码示例

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