scrapy框架一个相对完善的爬虫

用命令先生成自己的爬虫框架

scrapy startproject myspider

cd myspider

scrapy genspider itcast itcast.com

#itcast.py


# -*- coding: utf-8 -*-
import scrapy

from mySpider.items import ItcastItem

#所有爬虫的基类，用户定义的爬虫必须从这个类继承

from scrapy import log, Request
from scrapy.utils.trackref import object_ref
from scrapy.utils.url import url_is_from_spider

class ItcastSpider(scrapy.Spider):
    name = 'itcast'#爬虫名字，必须是唯一的，在不同的爬虫必须定义不同的名字。
    allowed_domains = ['itcast.cn']
#allow_domains = [] 是搜索的域名范围，也就是爬虫的约束区域，
# 规定爬虫只爬取这个域名下的网页，不存在的URL会被忽略。
    start_urls = ("http://www.itcast.cn/channel/teacher.shtml",)
#start_urls = () ：爬取的URL元祖/列表。爬虫从这里开始抓取数据，
# 所以，第一次下载的数据将会从这些urls开始。其他子URL将会
# 从这些起始URL中继承性生成
    def parse(self, response):
        '''
 parse(self, response) ：解析的方法，每个初始URL完成下载后将被调用，
 调用的时候传入从每一个URL传回的Response对象来作为唯一参数，主要作用如下：
1，负责解析返回的网页数据(response.body)，提取结构化数据(生成item)
2，生成需要下一页的URL请求。
def parse(self, response):
    filename='teacher.html'
    with open(filename,'w')as f:
        f.write(response.text)
然后运行一下看看，在mySpider目录下执行
scrapy crawl itcast

是的，就是 itcast，看上面代码，它是 ItcastSpider 类的 name 属性，也就是使用 scrapy genspider命令的唯一爬虫名。

运行之后，如果打印的日志出现 [scrapy] INFO: Spider closed (finished)，代表执行完成。 之后当前文件夹中就出现了一个 teacher.html 文件，
里面就是我们刚刚要爬取的网页的全部源代码信息。

我们之前在mySpider/items.py 里定义了一个ItcastItem类。 这里引入进来
from mySpider.items import ItcastItem

然后将我们得到的数据封装到一个 ItcastItem 对象中，可以保存每个老师的属性


'''
        #存放老师信息的集合
        items=[]
        for each in response.xpath("//div[@class='li_txt']"):
            # 将我们得到的数据封装到一个 `ItcastItem` 对象
            item = ItcastItem()
            # extract()方法返回的都是unicode字符串
            name = each.xpath("h3/text()").extract()
            title = each.xpath("h4/text()").extract()
            info = each.xpath("p/text()").extract()

            # xpath返回的是包含一个元素的列表
            item['name'] = name[0]
            item['title'] = title[0]
            item['info'] = info[0]

            items.append(item)

            yield item#经过管道处理数据

        #     # 直接返回最后数据,不经过pipwline
        # return items

item.py

# -*- 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
'''
Item 定义结构化数据字段，用来保存爬取到的数据，
有点像Python中的dict，但是提供了一些额外的保护减少错误。
'''
class ItcastItem(scrapy.Item):
    name = scrapy.Field()
    level = scrapy.Field()
    title=scrapy.Field()
    info = scrapy.Field()

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
'''
    当Item在Spider中被收集之后，它将会被传递到Item Pipeline，这些Item Pipeline组件按定义的顺序处理Item。
每个Item Pipeline都是实现了简单方法的Python类，比如决定此Item是丢弃而存储。以下是item pipeline的一些典型应用：
验证爬取的数据(检查item包含某些字段，比如说name字段)
查重(并丢弃)
将爬取结果保存到文件或者数据库中

'''
import json
class ItcastJsonPipeline(object):
    '''
item写入JSON文件
以下pipeline将所有(从所有'spider'中)爬取到的item，
存储到一个独立地items.json 文件，每行包含一个序列化为'JSON'格式的
'item'

    '''

    def __init__(self):
        self.file = open('teacher.json', 'w+')

    def process_item(self, item, spider):
        content = json.dumps(dict(item), ensure_ascii=False) + "\n"
        self.file.write(content)
        return item

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

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

# Scrapy settings for mySpider 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 = 'mySpider'

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


# Crawl responsibly by identifying yourself (and your website) on the user-agent
#USER_AGENT = 'mySpider (+http://www.yourdomain.com)'

# 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 = 3
# 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 = {
#    'mySpider.middlewares.MyspiderSpiderMiddleware': 543,
#}

# Enable or disable downloader middlewares
# See https://doc.scrapy.org/en/latest/topics/downloader-middleware.html
DOWNLOADER_MIDDLEWARES = {
   # 'mySpider.middlewares.MyspiderDownloaderMiddleware': 543,
      'mySpider.middlewares.RandomUserAgent': 1,
    # 'mySpider.middlewares.RandomProxy': 100
}

# 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 = {
   'mySpider.pipelines.ItcastJsonPipeline': 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'
USER_AGENTS = [
    "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Win64; x64; Trident/5.0; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET CLR 2.0.50727; Media Center PC 6.0)",
    "Mozilla/5.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET CLR 1.0.3705; .NET CLR 1.1.4322)",
    "Mozilla/4.0 (compatible; MSIE 7.0b; Windows NT 5.2; .NET CLR 1.1.4322; .NET CLR 2.0.50727; InfoPath.2; .NET CLR 3.0.04506.30)",
    "Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN) AppleWebKit/523.15 (KHTML, like Gecko, Safari/419.3) Arora/0.3 (Change: 287 c9dfb30)",
    "Mozilla/5.0 (X11; U; Linux; en-US) AppleWebKit/527+ (KHTML, like Gecko, Safari/419.3) Arora/0.6",
    "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.2pre) Gecko/20070215 K-Ninja/2.1.1",
    "Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9) Gecko/20080705 Firefox/3.0 Kapiko/3.0",
    "Mozilla/5.0 (X11; Linux i686; U;) Gecko/20070322 Kazehakase/0.4.5"
    ]

middlewares.py

class RandomUserAgent(object):
    def process_request(self, request, spider):
        useragent = random.choice(USER_AGENTS)

        request.headers.setdefault("User-Agent", useragent)
其他没有更改

scrapy框架一个相对完善的爬虫

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