python简易爬虫

这篇文章主要讲解 python如何实现简易爬虫

爬虫流程

打开种子url —-> 获取种子url页面中所有的url —-> 判断是否被爬取过,未爬取过的url添加到url列表中 —-> 解析页面中需要的信息 —-> 写入数据库

上述流程中可以抽象出5个对象:

  • bootstrap 启动器
  • downloader 下载器
  • parser 解析器
  • url_manager url管理器
  • outputer 输出器

启动器(main.py)

先看启动器是如何实现的:

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#!/usr/bin/env python
# _*_ coding:utf-8 _*_
"""
Created on 2017/9/23
@author: tt
"""
import spider_outputer
import spider_parser
import spider_downloader
import spider_url_manager
class Main:
def __init__(self):
self.urls = spider_url_manager.UrlManager()
self.downloader = spider_downloader.Downloader()
self.outputer = spider_outputer.Outputer()
self.parser = spider_parser.Parser()
def craw(self, root_url):
self.urls.add_new_url(root_url)
count = 1
while self.urls.has_new_url():
try:
new_url = self.urls.get_new_url()
print('craw %d : %s' % (count, new_url))
html_content = self.downloader.download(new_url)
new_urls, new_data = self.parser.parser(new_url, html_content)
self.urls.add_new_urls(new_urls)
self.outputer.collect_data(new_data)
count += 1
except Exception as e:
print(e)
if __name__ == "__main__":
url = 'https://www.zhihu.com/people/li-xiao-miao-70/activities'
main = Main()
main.craw(url)

下载器(spider_downloader.py)

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#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Created on 2017/9/23
@author: tt
"""
import string
from urllib import request
from urllib.parse import quote
user_agent = 'Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36'
class Downloader:
def download(self, url):
if url is None:
return None
_url = quote(url, safe=string.printable)
req = request.Request(_url, headers={'User-Agent': user_agent})
response = request.urlopen(req)
if response.getcode() != 200:
print("request bad")
return None
html = response.read()
return html.decode('utf8')

解析器(spider_parser.py)

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#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Created on 2017/9/23
@author: tt
"""
from urllib import parse
from bs4 import BeautifulSoup
import user_info
class Parser:
def parser(self, page_url, html_content):
if page_url is None or html_content is None:
return
soup = BeautifulSoup(html_content, "html.parser")
new_urls = self._get_new_urls(page_url, soup)
new_data = self._get_new_data(page_url, soup)
return new_urls, new_data
def _get_new_urls(self, page_url, soup):
new_urls = set()
links = soup.find_all('a')
for link in links:
new_url = link.get('href')
new_full_url = parse.urljoin(page_url, new_url)
new_urls.add(new_full_url)
return new_urls
def _get_new_data(self, page_url, soup):
ret_data = []
author_infos = soup.find_all(class_='AuthorInfo')
print(len(author_infos))
for author_info in author_infos:
user_id = author_info.find(class_='UserLink-link').get('href')
user_id = user_id[user_id.find('e/') + 2:]
photo = author_info.find(class_='AuthorInfo-avatar').get('srcset')
pos = photo.find(' ')
photo = photo[:pos]
name = author_info.find('meta', attrs={"itemprop": "name"}).get('content')
profession = author_info.find(class_='AuthorInfo-badgeText').get_text()
user = user_info.UserInfo(user_id, name, photo, profession)
ret_data.append(user)
return ret_data

url管理器(spider_url_manager.py)

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#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Created on 2017/9/23
@author: tt
"""
class UrlManager:
def __init__(self):
self.visited_url = set()
self.visit_url = set()
def add_new_url(self, url):
if url is None:
return
if url not in self.visit_url and url not in self.visited_url:
self.visit_url.add(url)
def has_new_url(self):
return len(self.visit_url) != 0
def add_new_urls(self, urls):
if urls is None or len(urls) == 0:
return
for url in urls:
self.add_new_url(url)
def get_new_url(self):
new_url = self.visit_url.pop()
self.visited_url.add(new_url)
return new_url

输出器(spider_outputer.py)

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#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Created on 2017/9/23
@author: tt
"""
import user_dao
class Outputer:
def __init__(self):
self.user_dao = user_dao.UserDao()
def collect_data(self, data):
if data is None:
print('None')
return
else:
for d in data:
self.user_dao.add_user(d)

其他类

###数据库帮助类(db_helper.py)

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#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Created on 2017/9/23
@author: tt
"""
import pymysql
class DbHelper:
def _get_connection(self):
return pymysql.Connect(host='127.0.0.1', user='root', passwd='root', db='crawler', port=3306, charset='utf8')
def execute_update(self, sql, params):
connectin = self._get_connection()
cursor = connectin.cursor()
try:
if params is None:
s = sql
else:
s = (sql % params)
result = cursor.execute(s)
connectin.commit()
print('rows:', result)
except Exception as e:
print(e)
connectin.rollback()
finally:
cursor.close()
connectin.close()
def query(self, sql, params=None):
connection = self._get_connection()
cursor = connection.cursor()
try:
if params is None:
s = sql
else:
s = (sql % params)
cursor.execute(s)
rows = cursor.fetchall()
for row in rows:
print(row)
except Exception as e:
print(e)
connection.rollback()
finally:
cursor.close()
connection.close()

用户数据访问类(user_dao.py)

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#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Created on 2017/9/23
@author: tt
"""
import db_helper
class UserDao:
def __init__(self):
self.db = db_helper.DbHelper()
def add_user(self, user):
sql = '''INSERT IGNORE INTO zhihu_user(user_id, photo, name, profession) values('%s', '%s', '%s', '%s')'''
params = (user.user_id, user.photo, user.name, user.profession)
self.db.execute_update(sql=sql, params=params)

用户信息类(user_info.py)

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#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Created on 2017/9/23
@author: tt
"""
class UserInfo:
def __init__(self, user_id, name, photo, profession):
self.user_id = user_id
self.name = name
self.photo = photo
self.profession = profession
def __str__(self):
return 'UserInfo(name=' + self.name + ', photo=' + self.photo + ", profession=" + self.profession + ')\n'
def __repr__(self):
return self.__str__()

在python中print在输出对象是调用的是对象的__str__函数

这个小的demo爬取的是知乎用户id,头像,名称,职业信息