表达式 描述
nodename    选取此节点的所有子节点。
/   从根节点选取。
//  从匹配选择的当前节点选择文档中的节点，而不考虑它们的位置。
.   选取当前节点。
..  选取当前节点的父节点。
@   选取属性。

小案例

from lxml.html import etree
import requests,re

#http://all.hengyan.com/1/0_0_0_0_0_0_0_0_0_1.aspx
#http://all.hengyan.com/1/0_0_0_0_0_0_0_0_0_2.aspx
#http://all.hengyan.com/1/0_0_0_0_0_0_0_0_0_3.aspx

class HengYanSpider(object):

def __init__(self):
    self.first_url = 'http://all.hengyan.com/1/0_0_0_0_0_0_0_0_0_1.aspx'
    self.default_headers = {
        'User-Agent':'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.132 Safari/537.36'
    }

def get_noval_url(self,url=None):
    url = self.first_url if not url else url
    """获取小说详情的url地址"""
    html = self.send_request(url)
    if html:
        #解析数据(获取xpath解析器)
        etree_html = etree.HTML(html)
        print(etree_html)
        noval_urls = etree_html.xpath('//li[@class="bookname"]/a[1]/@href')
        for noval_url in noval_urls:
            print(noval_url)
            self.get_noval_detail(noval_url)

        if '下一页' in html:
            print('22222222222222222222222222222222222222')
            pattern = int(self.extract_first(etree_html.xpath('//span[@class="pageBarCurrentStyle"]/text()')))
            next_page = pattern + 1
            next_url = re.sub('\d+.aspx',str(next_page)+'.aspx',url)
            self.get_noval_url(next_url)
        else:
            print('空')
    else:
        print('数据获取失败')

def get_noval_detail(self,noval_url):
    """获取书籍详情的页面内容,解析数据"""
    html = self.send_request(noval_url)
    if html:
        # 解析数据(获取xpath解析器)
        etree_html = etree.HTML(html)
        # print('得到了详情页面')
        noval_dict = {}
        #书号
        book_id = self.extract_first(etree_html.xpath('//div[@class="dh"]/p/label/text()'))
        noval_dict['book_id'] = re.search('\d+',book_id).group()
        #热度
        noval_dict['hot'] = self.extract_first(etree_html.xpath('//p[@class="wendu"]/b/text()'))
        #火车票
        noval_dict['hot_track'] = self.extract_first(etree_html.xpath('//div[@class="piao"]/p[2]/span[@class="huocolor"]/text()'))
        #冰票
        noval_dict['bing_track'] = self.extract_first(etree_html.xpath('//div[@class="piao"]/p[2]/span[@class="bingcolor"]/text()'))
        #金笔
        noval_dict['jingbi'] = self.extract_first(etree_html.xpath('//div[@class="jinbi"]//li[1]/p[2]/text()'))
        #标题
        noval_dict['title'] = self.extract_first(etree_html.xpath('//h2/text()'))
        #简介
        noval_dict['content'] = self.extract_first(etree_html.xpath('//p[@class="intro ih1"]/text()|//p[@class="intro ih2"]/text()')).replace('\u3000','')
        #作者
        noval_dict['author'] = self.extract_first(etree_html.xpath('//div[@id="ainfo"]/p/span/a[2]/text()'))

        print(noval_dict)
        # print(len(noval_dict))

        self.save_data(noval_dict)


def save_data(self,noval_dict):
    """保存数据"""
    pass

def extract_first(self,data,default=''):
    if len(data) > 0:
        return data[0]
    return default

def send_request(self,url,header=None,data=None,method="GET"):
    """发送请求"""
    header = self.default_headers if not header else header


    if method == 'GET':
        #发送get请求
        response = requests.get(url=url,params=data,headers=header)
    else:
        #发送post请求
        response = requests.post(url=url, data=data, headers=header)

    if response.status_code == 200:
        #请求成功，返回页面源码
        return response.text


if __name__ == '__main__':

spider = HengYanSpider()
spider.get_noval_url()