随想录（scrapy入门）

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    很多时候需要从网站上面下载一些数据，没有爬虫的帮助其实还是很困难的。好在现在有各种各样的爬虫框架，程序员不需要自己编写很多的代码就可以构建一个简单的爬虫代码，十分方便。不管是自己喜欢的电影，还是时事新闻、视频，有一个爬虫不停帮你抓取最新消息，体验还是很不错的。本文参考了这个链接，上面的内容很不错，可以很快地看到爬虫效果。

 

1、安装scrapy

pip instal scrapy

如果安装有困难，可以直接安装whl文件。

 

2、创建工程

scrapy startproject douban

 

3、创建爬虫

cd douban
scrapy genspider douban_spider movie.douban.com

 

4、更新爬虫文件douban_spider.py

# -*- coding: utf-8 -*-
import scrapy
from douban.items import DoubanItem


class DoubanSpiderSpider(scrapy.Spider):
    name = 'douban_spider'
    allowed_domains = ['movie.douban.com']
    start_urls = ['https://movie.douban.com/top250']

    def parse(self, response):
        movie_list = response.xpath("//div[@class='article']//ol[@class='grid_view']/li")
        for i_item in movie_list:
            douban_item = DoubanItem()
            douban_item['serial_number'] = i_item.xpath("./div[@class='item']//em/text()").extract_first()
            douban_item['movie_name'] =  i_item.xpath(".//div[@class='info']/div[@class='hd']/a/span[1]/text()").extract_first()
            content = i_item.xpath(".//div[@class='bd']/p[1]/text()").extract()
            for i_content in content:
                content_s = "".join(i_content.split())
                douban_item['introduce'] = content_s
            douban_item['star'] = i_item.xpath(".//span[contains(@class,'rating_num')]/text()").extract_first()
            douban_item['evaluate'] = i_item.xpath(".//div[@class='star']//span[4]/text()").extract_first()
            douban_item['describe'] = i_item.xpath(".//p[@class='quote']/span/text()").extract_first()
            yield douban_item
        next_link = response.xpath("//span[@class='next']/link/@href").extract()
        if next_link:
            next_link = next_link[0]
            yield scrapy.Request("https://movie.douban.com/top250"+next_link,callback=self.parse)

 

5、 更新items.py文件

# -*- coding: utf-8 -*-

# Define here the models for your scraped items
#
# See documentation in:
# https://doc.scrapy.org/en/latest/topics/items.html

import scrapy

class DoubanItem(scrapy.Item):
    # define the fields for your item here like:
    serial_number = scrapy.Field()
    movie_name = scrapy.Field()
    introduce = scrapy.Field()
    star = scrapy.Field()
    evaluate = scrapy.Field()
    describe = scrapy.Field()

 

6、更新settings.py文件

# -*- coding: utf-8 -*-

# Scrapy settings for douban project
#
# For simplicity, this file contains only settings considered important or
# commonly used. You can find more settings consulting the documentation:
#
#     https://doc.scrapy.org/en/latest/topics/settings.html
#     https://doc.scrapy.org/en/latest/topics/downloader-middleware.html
#     https://doc.scrapy.org/en/latest/topics/spider-middleware.html

BOT_NAME = 'douban'

SPIDER_MODULES = ['douban.spiders']
NEWSPIDER_MODULE = 'douban.spiders'


# Crawl responsibly by identifying yourself (and your website) on the user-agent
USER_AGENT = 'Mozilla/5.0(iPhone;U;CPUiPhoneOS4_3_3likeMacOSX;en-us)AppleWebKit/533.17.9(KHTML,likeGecko)Version/5.0.2Mobile/8J2Safari/6533.18.5'

# Obey robots.txt rules
ROBOTSTXT_OBEY = False

# Configure maximum concurrent requests performed by Scrapy (default: 16)
#CONCURRENT_REQUESTS = 32

# Configure a delay for requests for the same website (default: 0)
# See https://doc.scrapy.org/en/latest/topics/settings.html#download-delay
# See also autothrottle settings and docs
DOWNLOAD_DELAY = 0.5
# The download delay setting will honor only one of:
#CONCURRENT_REQUESTS_PER_DOMAIN = 16
#CONCURRENT_REQUESTS_PER_IP = 16

# Disable cookies (enabled by default)
#COOKIES_ENABLED = False

# Disable Telnet Console (enabled by default)
#TELNETCONSOLE_ENABLED = False

# Override the default request headers:
#DEFAULT_REQUEST_HEADERS = {
#   'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
#   'Accept-Language': 'en',
#}

# Enable or disable spider middlewares
# See https://doc.scrapy.org/en/latest/topics/spider-middleware.html
#SPIDER_MIDDLEWARES = {
#    'douban.middlewares.DoubanSpiderMiddleware': 543,
#}

# Enable or disable downloader middlewares
# See https://doc.scrapy.org/en/latest/topics/downloader-middleware.html
#DOWNLOADER_MIDDLEWARES = {
#    'douban.middlewares.DoubanDownloaderMiddleware': 543,
#}

# Enable or disable extensions
# See https://doc.scrapy.org/en/latest/topics/extensions.html
#EXTENSIONS = {
#    'scrapy.extensions.telnet.TelnetConsole': None,
#}

# Configure item pipelines
# See https://doc.scrapy.org/en/latest/topics/item-pipeline.html
#ITEM_PIPELINES = {
#    'douban.pipelines.DoubanPipeline': 300,
#}

# Enable and configure the AutoThrottle extension (disabled by default)
# See https://doc.scrapy.org/en/latest/topics/autothrottle.html
#AUTOTHROTTLE_ENABLED = True
# The initial download delay
#AUTOTHROTTLE_START_DELAY = 5
# The maximum download delay to be set in case of high latencies
#AUTOTHROTTLE_MAX_DELAY = 60
# The average number of requests Scrapy should be sending in parallel to
# each remote server
#AUTOTHROTTLE_TARGET_CONCURRENCY = 1.0
# Enable showing throttling stats for every response received:
#AUTOTHROTTLE_DEBUG = False

# Enable and configure HTTP caching (disabled by default)
# See https://doc.scrapy.org/en/latest/topics/downloader-middleware.html#httpcache-middleware-settings
#HTTPCACHE_ENABLED = True
#HTTPCACHE_EXPIRATION_SECS = 0
#HTTPCACHE_DIR = 'httpcache'
#HTTPCACHE_IGNORE_HTTP_CODES = []
#HTTPCACHE_STORAGE = 'scrapy.extensions.httpcache.FilesystemCacheStorage'

 

7、执行爬虫或者保存爬虫结果（区别就是有没有-o选项）

cd douban
scrapy crawl douban_spider 
scrapy crawl douban_spider -o douban.csv
scrapy crawl douban_spider -o douban.json

 

8、优化爬虫

优化爬虫的主要思路就是如何处理404、用户名登陆、ip代理、数据过滤、js获取数据这些。

根据不同的网站和不同的需求，可以灵活做出修改。

 

9、合法使用爬虫

现在各大网站上有价值的数据很多，但一定要合法使用爬虫，不要用于非法目的，也不要对服务器造成太大的影响。

 

注：

除了上面提到的三个python文件之外，一般还有pieplines.py和middlewares.py。前者通常用于数据保存，比如将获取的item保存到本地或者远程数据库中。后者多用来处理各种各样的异常情况，比如js数据访问、cookie、ip代理、数字和符号识别、账户密码登录等等。