python Scrapy 从零开始学习笔记（一）

在之前我做了一个系列的关于 python 爬虫的文章，传送门：https://www.cnblogs.com/weijiutao/p/10735455.html，并写了几个爬取相关网站并提取有效信息的案例：https://www.cnblogs.com/weijiutao/p/10614694.html 等，从本章开始本人将继续深入学习 python 爬虫，主要是基于 Scrapy 库展开，特此记录，与君共勉！

Scrapy 官方网址：https://docs.scrapy.org/en/latest/

Scrapy 中文网址：https://scrapy-chs.readthedocs.io/zh_CN/latest/index.html

Scrapy 框架

• Scrapy是用纯Python实现一个为了爬取网站数据、提取结构性数据而编写的应用框架，用途非常广泛。

• 框架的力量，用户只需要定制开发几个模块就可以轻松的实现一个爬虫，用来抓取网页内容以及各种图片，非常之方便。

• Scrapy 使用了 Twisted['twɪstɪd](其主要对手是Tornado)异步网络框架来处理网络通讯，可以加快我们的下载速度，不用自己去实现异步框架，并且包含了各种中间件接口，可以灵活的完成各种需求。

Scrapy架构图(绿线是数据流向)：

• Scrapy Engine(引擎): 负责Spider、ItemPipeline、Downloader、Scheduler中间的通讯，信号、数据传递等。

• Scheduler(调度器): 它负责接受引擎发送过来的Request请求，并按照一定的方式进行整理排列，入队，当引擎需要时，交还给引擎。

• Downloader（下载器）：负责下载Scrapy Engine(引擎)发送的所有Requests请求，并将其获取到的Responses交还给Scrapy Engine(引擎)，由引擎交给Spider来处理，

• Spider（爬虫）：它负责处理所有Responses,从中分析提取数据，获取Item字段需要的数据，并将需要跟进的URL提交给引擎，再次进入Scheduler(调度器)，

• Item Pipeline(管道)：它负责处理Spider中获取到的Item，并进行进行后期处理（详细分析、过滤、存储等）的地方.

• Downloader Middlewares（下载中间件）：你可以当作是一个可以自定义扩展下载功能的组件。

• Spider Middlewares（Spider中间件）：你可以理解为是一个可以自定扩展和操作引擎和Spider中间通信的功能组件（比如进入Spider的Responses;和从Spider出去的Requests）

以上是 Scrapy 的架构图，从流程上看还是很清晰的，我就只简单的说一下，首先从红色方框的 Spider 开始，通过引擎发送给调度器任务，再将请求任务交给下载器并处理完后返回结果给 Spider，最后将结果交给关到来处理我们的结果就可以了。

上面的话可能还是会有些拗口，在接下来我们会一点点进行剖析，最后会发现利用 Scrapy 框架来做爬虫是如此简单。

Scrapy的安装

windows 安装  pip install scrapy 

Mac 安装  sudo pip install scrapy 

pip 升级  pip install --upgrade pip 

本人目前使用的是Mac电脑，目前使用的是 python3 版本，内容上其实都大同小异，如遇系统或版本问题可及时联系，互相学习！

安装完成后我们在终端输出 Scrapy 即可安装是否成功：

新建项目

在 Scrapy 安装成功之后，我们就需要用它来开发我们的爬虫项目了，进入自定义的项目目录中，运行下列命令：

 scrapy startproject spiderDemo 

运行上面的命令行就会在我们项目目录下生成一下目录结构：

 下面来简单介绍一下各个主要文件的作用：

scrapy.cfg ：项目的配置文件

scrapyDemo/ ：项目的Python模块，将会从这里引用代码

scrapyDemo/items.py ：项目的目标文件

scrapyDemo/middlewares.py ：项目的中间件文件

scrapyDemo/pipelines.py ：项目的管道文件

scrapyDemo/settings.py ：项目的设置文件

scrapyDemo/spiders/ ：存储爬虫代码目录

接下来我们对各文件里的内容简单说一下，里面的代码目前都是最简单的基本代码，在接下来做案例的时候我们会再有针对地对文件做一下解释。

其中的 __init_.py 文件内容都是空的，但是却不能删除掉，否则项目将无法启动。

spiderDemo/items.py

# -*- 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 ScrapydemoItem(scrapy.Item):
    # define the fields for your item here like:
    # name = scrapy.Field()
    pass

该文件是用来定义我们通过爬虫所获取到的有用的信息，即 scrapy.Item

scrapyDemo/middlewares.py

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

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

from scrapy import signals


class ScrapydemoSpiderMiddleware(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 spiders.
        s = cls()
        crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
        return s

    def process_spider_input(self, response, spider):
        # 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):
        # 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):
        # 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 ScrapydemoDownloaderMiddleware(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 spiders.
        s = cls()
        crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
        return s

    def process_request(self, request, spider):
        # 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):
        # 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):
        # 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)

该文件为中间件文件，名字后面的s表示复数，说明这个文件里面可以放很多个中间件，我们用到的中间件可以在此定义

spiderDemo/pipelines.py

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

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


class ScrapydemoPipeline(object):
    def process_item(self, item, spider):
        return item

该文件俗称管道文件，是用来获取到我们的Item数据，并对数据做针对性的处理。

scrapyDemo/settings.py

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

# Scrapy settings for scrapyDemo 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 = 'scrapyDemo'

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


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

# Obey robots.txt rules
ROBOTSTXT_OBEY = True

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

# Enable or disable downloader middlewares
# See https://docs.scrapy.org/en/latest/topics/downloader-middleware.html
#DOWNLOADER_MIDDLEWARES = {
#    'scrapyDemo.middlewares.ScrapydemoDownloaderMiddleware': 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
#ITEM_PIPELINES = {
#    'scrapyDemo.pipelines.ScrapydemoPipeline': 300,
#}

# 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'

该文件为我们的设置文件，一些基本的设置需要我们在此文件中进行配置，如我们的中间件文件当中的两个类 ScrapydemoSpiderMiddleware，ScrapydemoDownloaderMiddleware 在 settings.py 中就能找到。

在 settings 文件中，我们常会配置到如上面的字段 如：ITEM_PIPELINES（管道文件），DEFAULT_REQUEST_HEADERS（请求报头），DOWNLOAD_DELAY（下载延迟）

，ROBOTSTXT_OBEY（是否遵循爬虫协议）等。

本章我们就先简单的介绍一下 scrapy 的基本目录，下一章我们来根据 scrapy 框架实现一个爬虫案例。