scrapy.Spider的属性和方法
属性:
name:spider的名称,要求唯一
allowed_domains:允许的域名,限制爬虫的范围
start_urls:初始urls
custom_settings:个性化设置,会覆盖全局的设置
crawler:抓取器,spider将绑定到它上面
custom_settings:配置实例,包含工程中所有的配置变量
logger:日志实例,打印调试信息

方法:
from_crawler(crawler, *args, **kwargs):类方法,用于创建spider
start_requests():生成初始的requests
make_requests_from_url(url):遍历urls,生成一个个request
parse(response):用来解析网页内容
log(message[,level.component]):用来记录日志,这里请使用logger属性记录日志,self.logger.info(‘visited success‘)
closed(reason):当spider关闭时调用的方法

子类:
主要CrawlSpider
1:最常用的spider,用于抓取普通的网页
2:增加了两个成员
1)rules:定义了一些抓取规则--链接怎么跟踪,使用哪一个parse函数解析此链接
2)parse_start_url(response):解析初始url的相应
实例:
import scrapy
from scrapy.spiders import CrawlSpider, Rule
from scrapy.linkextractors import LinkExtractor

class MySpider(CrawlSpider):
    name = ‘example.com‘
    allowed_domains = [‘example.com‘]
    start_urls = [‘http://www.example.com‘]

    rules = (
        # Extract links matching ‘category.php‘ (but not matching ‘subsection.php‘)
        # and follow links from them (since no callback means follow=True by default).
        Rule(LinkExtractor(allow=(‘category\.php‘, ), deny=(‘subsection\.php‘, ))),

        # Extract links matching ‘item.php‘ and parse them with the spider‘s method parse_item
        Rule(LinkExtractor(allow=(‘item\.php‘, )), callback=‘parse_item‘),
    )

    def parse_item(self, response):
        self.logger.info(‘Hi, this is an item page! %s‘, response.url)
        item = scrapy.Item()
        item[‘id‘] = response.xpath(‘//td[@id="item_id"]/text()‘).re(r‘ID: (\d+)‘)
        item[‘name‘] = response.xpath(‘//td[@id="item_name"]/text()‘).extract()
        item[‘description‘] = response.xpath(‘//td[@id="item_description"]/text()‘).extract()
        return item