scrapy入门例子

使用爬取http://quotes.toscrape.com/内容，网站内容很简单

一. 使用scrapy创建项目

scrapy startproject myscrapy1

scrapy genspider quotes

二. 修改items.py和quotes.py

items.py用来保存爬取的数据，和字典的使用方法一样

import scrapy

class Myscrapy1Item(scrapy.Item):
    # define the fields for your item here like:
    text = scrapy.Field()
    author = scrapy.Field()
    tags = scrapy.Field()

网页源文件中只需提取上面定义的3个字段

 

quotes.py

其中的parse函数负责解析start_urls返回的响应，提取数据以及进一步生成要处理的请求

# -*- coding: utf-8 -*-
import scrapy
from myscrapy1.items import Myscrapy1Item

class QuotesSpider(scrapy.Spider):
    name = 'quotes'
    allowed_domains = ['quotes.toscrape.com']
    start_urls = ['http://quotes.toscrape.com/']

    def parse(self, response):
        quotes = response.css('.quote')
        for quote in quotes:
            item = Myscrapy1Item()

            item['text'] = quote.css('.text::text').extract_first()
            item['author'] = quote.css('.author::text').extract_first()
            item['tags'] = quote.css('.tags .tag::text').extract()
            yield item

        #获取多页内容
        next = response.css('.pager .next a::attr("href")').extract_first()
        url = response.url.join(next) #生成绝对URL
        yield scrapy.Request(url=url, callback=self.parse) #构造请求时需要用scrapy.Request

二. 将数据保存到mongodb，以及把得到的数据限制显示50位，剩余的用省略号代替，这里需要设置settings.py和pipelines.py

settings.py

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


BOT_NAME = 'tutorial'

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

#让pipelines.py中的2个自定义类生效,序号越小优先级越高
ITEM_PIPELINES = {
    'tutorial.pipelines.TextPipeline': 300,
    'tutorial.pipelines.MongoPipeline': 400,
}

MONGO_URI='localhost'
MONGO_DB='tutorial'

  # Obey robots.txt rules
  ROBOTSTXT_OBEY = True

pipelines.py

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

# Define your item pipelines here
#
# Don't forget to add your pipeline to the ITEM_PIPELINES setting
# See: https://doc.scrapy.org/en/latest/topics/item-pipeline.html

# 文本太长，限制最长为50，后面用省略号代替

from scrapy.exceptions import DropItem
import pymongo


class TextPipeline(object):
    def __init__(self):
        self.limit = 50

    def process_item(self, item, spider):
        if item['text']:
            if len(item['text']) > self.limit:
                item['text'] = item['text'][0:self.limit].rstrip() + '...'
            return item
        else:
            return DropItem('Missing Text') #文本不存在，抛出异常MISSING TEXT


# 保存到mongodb
class MongoPipeline(object):
    
    def __init__(self,mongo_uri, mongo_db):
        self.mongo_uri = mongo_uri
        self.mongo_db = mongo_db
    
    #从setting.py中拿到配置信息
    @classmethod
    def from_crawler(cls, crawler):
        return cls(
            mongo_uri=crawler.settings.get('MONGO_URI'),
            mongo_db=crawler.settings.get('MONGO_DB')
        )

    def open_spider(self, spider):
        self.client = pymongo.MongoClient(self.mongo_uri)
        self.db = self.client[self.mongo_db]

    def process_item(self, item, spider):
        name = item.__class__.__name__ #其实值就是quotes
        self.db[name].insert(dict(item))
        return item

    def close_spider(self, spider):
        self.client.close()

三. 常用的几个命令

1.创建一个爬虫项目 
scrapy startproject test1

2. 生成一个爬虫文件
scrapy genspider baidu www.baidu.com

scrapy genspider -l :显示爬虫模板类型
例如：指定生成一个crawl 模板类型的爬虫文件
scrapy genspider -t crawl zhihu www.zhihu.com

3. 运行爬虫程序
scrapy crawl zhihu

4. 检查代码是否有错误
scrapy check

5. 返回项目中所有spider名称
scrapy list


6. 爬取内容保存到文件
scrapy crawl zhihu -o zhihu.json