Python爬虫之scrapy框架使用详解

Python爬虫之scrapy框架使用详解

1. scrapy框架命令

<<全局命令>>（全局命令可以在任何地方使用）
1. scrapy startproject <project_name>               # 创建爬虫项目
2. scrapy genspider [-t template] <name> <domain>   # 创建爬虫文件
3. scrapy runspider <spider_file.py>                # 直接通过运行.py文件来启动爬虫
4. scrapy shell [url]                               # 打开scrapy-shell交互器（可以使用Selector进行调试）
5. scrapy fetch <url>                               # 该命令会通过scrapy-downloader将网页的源代码下载并显示出来
6. settings           # 查看项目设置
7. version            # 查看版本
8. view               # 该命令会将网页document内容下载下来，并且在浏览器显示出来（可以判断是否是Ajax请求）


<<项目命令>>（项目命令只能在项目目录下使用）
1. scrapy crawl <spider>      # 启动爬虫程序
2. scrapy list                # 显示项目中所有的爬虫
3. check                      # 用于检查代码是否有错误
4. edit                       # 编辑
5. parse                      # 解析调试
6. bench                      # 速度测试


<<创建示例>>（如果命令显示无效，在命令前面加上“python -m”）
1. scrapy startproject example  # 创建名字为example的项目
2. cd example  # 切换到该项目
3. scrapy genspider sample_spider www.sample.com  # 创建名字为sample_spider的爬虫文件，并且初始域名为www.sample.com
4. scrapy crawl sample  # 执行sample爬虫程序
5. scrapy crawl sample -o sample.json  # 保存输出结果到json文件（还有csv，xml，pickle，marshal，ftp等格式可以存取）

scrapy crawl sample --nolog  # 不打印日志
scrapy crawl sample --headers  # 打印响应头信息
scrapy crawl sample --no-redirect  # 不做跳转（禁止重定向）

<<shell调试>>
python3 -m scrapy shell
response.selector.xpath('')
response.selector.css('')

2. scrapy项目文件结构

创建一个名叫example的scrapy项目，并且添加一个sample_spider.py
文件结构如下：

接下来对scrapy项目内的每个文件进行讲解
使用方法都写在程序里面的注释中，请尽情享用，如果您觉得不错可以点个赞哦

2.1 sample_spider

"""Spider类基础属性和方法
属性:                       含义:
name                       爬虫名称，它必须是唯一的，用来启动爬虫
allowed_domains            允许爬取的域名，是可选配置
start_urls                 起始URL列表，当没有重写start_requests()方法时，默认使用这个列表
custom_settings            它是一个字典，专属与本Spider的配置，此设置会覆盖项目全局的设置，必须在初始化前被更新，必须定义成类变量
spider                     它是由from_crawler()方法设置的，代表本Spider类对应的Crawler对象，可以获取项目的全局配置信息
settings                   它是一个Settings对象，我们可以直接获取项目的全局设置变量

方法：                      含义:
start_requests()           生成初始请求，必须返回一个可迭代对象，默认使用start_urls里的URL和GET请求，如需使用POST需要重写此方法
parse()                    当Response没有指定回调函数时，该方法会默认被调用，该函数必须要返回一个包含Request或Item的可迭代对象
closed()                   当Spider关闭时，该方法会被调用，可以在这里定义释放资源的一些操作或其他收尾操作

Request属性：
meta                       可以利用Request请求传入参数，在Response中可以取值，是一个字典类型
cookies                    可以传入cookies信息，是一个字典类型
dont_filter                如果使用POST，需要多次提交表单，且URL一样，那么就必须设置为True，防止被当成重复网页过滤掉
"""
# -*- coding: utf-8 -*-
import scrapy

from ..items import ExampleItem
from scrapy.http import Request, FormRequest
from scrapy import Selector

__author__ = 'Evan'


class SampleSpider(scrapy.Spider):
    name = 'sample_spider'  # 项目名称，具有唯一性不能同名
    allowed_domains = ['quotes.toscrape.com']  # 允许的domain range
    start_urls = ['http://quotes.toscrape.com/']  # 起始URL

    """更改初始请求，必须返回一个可迭代对象
    def start_requests(self):
        return [Request(url=self.start_urls[0], callback=self.parse)]
        or
        yield Request(url=self.start_urls[0], callback=self.parse)
    """

    def parse(self, response):
        """
        当Response没有指定回调函数时，该方法会默认被调用
        :param response: From the start_requests() function
        :return: 该函数必须要返回一个包含 Request 或 Item 的可迭代对象
        """
        # TODO Request attribute
        # print(response.request.url)  # 返回Request的URL
        # print(response.request.headers)  # 返回Request的headers
        # print(response.request.headers.getlist('Cookie'))  # 返回Request的cookies

        # TODO Response attribute
        # print(response.text)  # 返回Response的HTML
        # print(response.body)  # 返回Response的二进制格式HTML
        # print(response.url)  # 返回Response的URL
        # print(response.headers)  # 返回Response的headers
        # print(response.headers.getlist('Set-Cookie'))  # 返回Response的cookies
        # json.loads(response.text)  # 获取AJAX数据，返回一个字典

        # TODO 使用Selector选择器
        # selector = Selector(response=response)  # 选择Response初始化
        # selector = Selector(text=div)  # 选择HTML文本初始化
        # selector.xpath('//a/text()').extract()  # 使用xpath选择器解析，返回一个列表
        # selector.xpath('//a/text()').re('Name:\s(.*)')  # 使用xpath选择器 + 正则表达式解析，返回正则匹配的分组列表
        # selector.xpath('//a/text()').re_first('Name:\s(.*)')  # 使用xpath选择器 + 正则表达式解析，返回正则匹配的第一个结果

        # TODO 从settings.py中获取全局配置信息
        # print(self.settings.get('USER_AGENT'))

        quotes = response.css('.quote')  # 使用css选择器，返回一个SelectorList类型的列表
        item = ExampleItem()
        for quote in quotes:
            # ::text  获取文本
            # ::attr(src)  获取src属性的值
            item['text'] = quote.css('.text::text').extract_first()  # 返回匹配到的第一个结果
            item['author'] = quote.css('.author::text').extract_first()
            item['tags'] = quote.css('.tags .tag::text').extract()  # 返回一个包含所有结果的列表
            yield item

        next_url = response.css('.pager .next a::attr("href")').extract_first()  # 返回下一页的URL
        url = response.urljoin(next_url)  # 拼接成一个绝对的URL
        yield Request(url=url, callback=self.parse)  # 设置回调函数，循环检索每一页

2.2 itmes

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

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

import scrapy


class ExampleItem(scrapy.Item):
    """
    定义数据结构
    """
    text = scrapy.Field()
    author = scrapy.Field()
    tags = scrapy.Field()

2.3 middlewares

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

# Define here the models for your spider middleware
#
# See documentation in:
# https://docs.scrapy.org/en/latest/topics/spider-middleware.html
import random
from scrapy import signals


class RandomUserAgentMiddleware(object):
    """
    自定义类
    """
    def __init__(self):
        self.user_agents = [
            # Chrome UA
            'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko)'
            ' Chrome/73.0.3683.75 Safari/537.36',
            # IE UA
            'Mozilla/5.0 (Windows NT 10.0; WOW64; Trident/7.0; rv:11.0) like Gecko',
            # Microsoft Edge UA
            'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko)'
            ' Chrome/64.0.3282.140 Safari/537.36 Edge/18.17763'
        ]

    def process_request(self, request, spider):
        """
        生成一个随机请求头
        :param request:
        :param spider:
        :return:
        """
        request.headers['User-Agent'] = random.choice(self.user_agents)


class ExampleSpiderMiddleware(object):
    # Not all methods need to be defined. If a method is not defined,
    # scrapy acts as if the spider middleware does not modify the
    # passed objects.

    @classmethod
    def from_crawler(cls, crawler):
        # This method is used by Scrapy to create your spider.
        s = cls()
        crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
        return s

    def process_spider_input(self, response, spider):
        """
        当 Response 被 Spider MiddleWare 处理时，会调用此方法
        :param response:
        :param spider:
        :return:
        """
        # Called for each response that goes through the spider
        # middleware and into the spider.

        # Should return None or raise an exception.
        return None

    def process_spider_output(self, response, result, spider):
        """
        当 Spider 处理 Response 返回结果时，会调用此方法
        :param response:
        :param result:
        :param spider:
        :return:
        """
        # Called with the results returned from the Spider, after
        # it has processed the response.

        # Must return an iterable of Request, dict or Item objects.
        for i in result:
            yield i

    def process_spider_exception(self, response, exception, spider):
        # Called when a spider or process_spider_input() method
        # (from other spider middleware) raises an exception.

        # Should return either None or an iterable of Request, dict
        # or Item objects.
        pass

    def process_start_requests(self, start_requests, spider):
        """
        以 Spider 启动的 Request 为参数被调用，执行的过程类似 process_spider_output()，必须返回 Request
        :param start_requests:
        :param spider:
        :return:
        """
        # Called with the start requests of the spider, and works
        # similarly to the process_spider_output() method, except
        # that it doesn’t have a response associated.

        # Must return only requests (not items).
        for r in start_requests:
            yield r

    def spider_opened(self, spider):
        spider.logger.info('Spider opened: %s' % spider.name)


class ExampleDownloaderMiddleware(object):
    # Not all methods need to be defined. If a method is not defined,
    # scrapy acts as if the downloader middleware does not modify the
    # passed objects.

    @classmethod
    def from_crawler(cls, crawler):
        # This method is used by Scrapy to create your spider.
        s = cls()
        crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
        return s

    def process_request(self, request, spider):
        """
        在发送请求到 Download 之前调用此方法，可以修改User-Agent、处理重定向、设置代理、失败重试、设置Cookies等功能
        :param request:
        :param spider:
        :return: 如果返回的是一个 Request，会把它放到调度队列，等待被调度
        """
        # Called for each request that goes through the downloader
        # middleware.

        # Must either:
        # - return None: continue processing this request
        # - or return a Response object
        # - or return a Request object
        # - or raise IgnoreRequest: process_exception() methods of
        #   installed downloader middleware will be called
        return None

    def process_response(self, request, response, spider):
        """
        在发送 Response 响应结果到 Spider 解析之前调用此方法，可以修改响应结果
        :param request:
        :param response:
        :param spider:
        :return: 如果返回的是一个 Request，会把它放到调度队列，等待被调度
        """
        # Called with the response returned from the downloader.

        # Must either;
        # - return a Response object
        # - return a Request object
        # - or raise IgnoreRequest
        return response

    def process_exception(self, request, exception, spider):
        """
        当 Downloader 或 process_request() 方法抛出异常时，会调用此方法
        :param request:
        :param exception:
        :param spider:
        :return: 如果返回的是一个 Request，会把它放到调度队列，等待被调度
        """
        # Called when a download handler or a process_request()
        # (from other downloader middleware) raises an exception.

        # Must either:
        # - return None: continue processing this exception
        # - return a Response object: stops process_exception() chain
        # - return a Request object: stops process_exception() chain
        pass

    def spider_opened(self, spider):
        spider.logger.info('Spider opened: %s' % spider.name)

2.4 pipelines

# -*- coding: utf-8 -*-
import pymongo
from scrapy.exceptions import DropItem


class TextPipeline(object):
    """
    自定义类
    """
    def __init__(self):
        self.limit = 50

    def process_item(self, item, spider):
        """
        必须要实现的方法，Pipeline会默认调用此方法
        :param item:
        :param spider:
        :return: 必须返回 Item 类型的值或者抛出一个 DropItem 异常
        """
        if item['text']:
            if len(item['text']) > self.limit:  # 对超过50个字节长度的字符串进行切割
                item['text'] = item['text'][:self.limit].rstrip() + '...'
            return item
        else:
            raise DropItem('Missing Text')  # 如果抛出此异常，会丢弃此Item，不再进行处理


class MongoPipeline(object):
    """
    自定义类
    """
    def __init__(self, mongo_uri, mongo_db):
        self.mongo_uri = mongo_uri
        self.mongo_db = mongo_db
        self.client = None
        self.db = None

    @classmethod
    def from_crawler(cls, crawler):
        """
        Pipelines的准备工作，通过crawler可以拿到全局配置的每个配置信息
        :param crawler:
        :return: 类实例
        """
        # 使用类方法，返回带有MONGO_URI和MONGO_DB值的类实例
        return cls(
            mongo_uri=crawler.settings.get('MONGO_URI'),  # MONGO_URI的值从settings.py获取
            mongo_db=crawler.settings.get('MONGO_DB')  # MONGO_DB的值从settings.py获取
        )

    def open_spider(self, spider):
        """
        当 Spider 开启时，这个方法会被调用
        :param spider:
        :return:
        """
        self.client = pymongo.MongoClient(self.mongo_uri)  # 打开Mongodb连接
        self.db = self.client[self.mongo_db]

    def process_item(self, item, spider):
        """
        必须要实现的方法，Pipeline会默认调用此方法
        :param item:
        :param spider:
        :return: 必须返回 Item 类型的值或者抛出一个 DropItem 异常
        """
        name = item.__class__.__name__  # 创建一个集合，name='ExampleItem'
        self.db[name].update_one(item, {
     "$set": item}, upsert=True)  # 数据去重
        return item

    def close_spider(self, spider):
        """
        当 Spider 关闭时，这个方法会被调用
        :param spider:
        :return:
        """
        self.client.close()  # 关闭Mongodb连接

2.5 settings

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

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

BOT_NAME = 'example'

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

# Crawl responsibly by identifying yourself (and your website) on the user-agent
# TODO 设置默认的用户代理请求头
USER_AGENT = 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) ' \
             'Chrome/78.0.3904.108 Safari/537.36'

# Obey robots.txt rules
# TODO 不请求Robots协议
ROBOTSTXT_OBEY = False

# TODO 设置编码格式
FEED_EXPORT_ENCODING = 'utf-8'  # 在json格式下转换中文编码
# FEED_EXPORT_ENCODING = 'gb18030'  # 在csv格式下转换中文编码

# 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://docs.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)
# TODO 如果设置为True则可以手动添加Cookies参数到Request请求中
COOKIES_ENABLED = True

# 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://docs.scrapy.org/en/latest/topics/spider-middleware.html
#SPIDER_MIDDLEWARES = {
     
#    'example.middlewares.ExampleSpiderMiddleware': 543,
#}

# Enable or disable downloader middlewares
# See https://docs.scrapy.org/en/latest/topics/downloader-middleware.html
# TODO 使用下载中间件，设置随机请求头
DOWNLOADER_MIDDLEWARES = {
     
   'example.middlewares.RandomUserAgentMiddleware': 543,
}

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

# Configure item pipelines
# See https://docs.scrapy.org/en/latest/topics/item-pipeline.html
# TODO 使用项目管道，过滤和保存数据（字典的value越小，优先级越高，如下所示：300优先级 > 400优先级）
ITEM_PIPELINES = {
     
   'example.pipelines.TextPipeline': 300,
   'example.pipelines.MongoPipeline': 400,
}
# TODO Mongodb配置
MONGO_URI = 'localhost'
MONGO_DB = 'example'

# Enable and configure the AutoThrottle extension (disabled by default)
# See https://docs.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://docs.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'

2.6 main

在编写完所有scrapy代码后，创建一个main.py来启动scrapy （直接运行main.py即可）

# -*- coding=utf8 -*-
from scrapy import cmdline

# TODO 执行爬虫指令
cmdline.execute("scrapy crawl sample_spider".split())  # 执行sample_spider爬虫
cmdline.execute("scrapy crawl sample_spider -o sample.json".split())  # 执行爬虫并在当前目录下生成一个sample.json文件（该文件是爬虫结果）