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')
