python Scrapy 从零开始学习笔记（一）

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

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• 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

 1 # -*- coding: utf-8 -*-
 2 
 3 # Define here the models for your scraped items
 4 #
 5 # See documentation in:
 6 # https://docs.scrapy.org/en/latest/topics/items.html
 7 
 8 import scrapy
 9 
10 
11 class ScrapydemoItem(scrapy.Item):
12     # define the fields for your item here like:
13     # name = scrapy.Field()
14     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

  1 # -*- coding: utf-8 -*-
  2 
  3 # Define here the models for your spider middleware
  4 #
  5 # See documentation in:
  6 # https://docs.scrapy.org/en/latest/topics/spider-middleware.html
  7 
  8 from scrapy import signals
  9 
 10 
 11 class ScrapydemoSpiderMiddleware(object):
 12     # Not all methods need to be defined. If a method is not defined,
 13     # scrapy acts as if the spider middleware does not modify the
 14     # passed objects.
 15 
 16     @classmethod
 17     def from_crawler(cls, crawler):
 18         # This method is used by Scrapy to create your spiders.
 19         s = cls()
 20         crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
 21         return s
 22 
 23     def process_spider_input(self, response, spider):
 24         # Called for each response that goes through the spider
 25         # middleware and into the spider.
 26 
 27         # Should return None or raise an exception.
 28         return None
 29 
 30     def process_spider_output(self, response, result, spider):
 31         # Called with the results returned from the Spider, after
 32         # it has processed the response.
 33 
 34         # Must return an iterable of Request, dict or Item objects.
 35         for i in result:
 36             yield i
 37 
 38     def process_spider_exception(self, response, exception, spider):
 39         # Called when a spider or process_spider_input() method
 40         # (from other spider middleware) raises an exception.
 41 
 42         # Should return either None or an iterable of Request, dict
 43         # or Item objects.
 44         pass
 45 
 46     def process_start_requests(self, start_requests, spider):
 47         # Called with the start requests of the spider, and works
 48         # similarly to the process_spider_output() method, except
 49         # that it doesn’t have a response associated.
 50 
 51         # Must return only requests (not items).
 52         for r in start_requests:
 53             yield r
 54 
 55     def spider_opened(self, spider):
 56         spider.logger.info('Spider opened: %s' % spider.name)
 57 
 58 
 59 class ScrapydemoDownloaderMiddleware(object):
 60     # Not all methods need to be defined. If a method is not defined,
 61     # scrapy acts as if the downloader middleware does not modify the
 62     # passed objects.
 63 
 64     @classmethod
 65     def from_crawler(cls, crawler):
 66         # This method is used by Scrapy to create your spiders.
 67         s = cls()
 68         crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
 69         return s
 70 
 71     def process_request(self, request, spider):
 72         # Called for each request that goes through the downloader
 73         # middleware.
 74 
 75         # Must either:
 76         # - return None: continue processing this request
 77         # - or return a Response object
 78         # - or return a Request object
 79         # - or raise IgnoreRequest: process_exception() methods of
 80         #   installed downloader middleware will be called
 81         return None
 82 
 83     def process_response(self, request, response, spider):
 84         # Called with the response returned from the downloader.
 85 
 86         # Must either;
 87         # - return a Response object
 88         # - return a Request object
 89         # - or raise IgnoreRequest
 90         return response
 91 
 92     def process_exception(self, request, exception, spider):
 93         # Called when a download handler or a process_request()
 94         # (from other downloader middleware) raises an exception.
 95 
 96         # Must either:
 97         # - return None: continue processing this exception
 98         # - return a Response object: stops process_exception() chain
 99         # - return a Request object: stops process_exception() chain
100         pass
101 
102     def spider_opened(self, spider):
103         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

 1 # -*- coding: utf-8 -*-
 2 
 3 # Define your item pipelines here
 4 #
 5 # Don't forget to add your pipeline to the ITEM_PIPELINES setting
 6 # See: https://docs.scrapy.org/en/latest/topics/item-pipeline.html
 7 
 8 
 9 class ScrapydemoPipeline(object):
10     def process_item(self, item, spider):
11         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

 1 # -*- coding: utf-8 -*-
 2 
 3 # Scrapy settings for scrapyDemo project
 4 #
 5 # For simplicity, this file contains only settings considered important or
 6 # commonly used. You can find more settings consulting the documentation:
 7 #
 8 #     https://docs.scrapy.org/en/latest/topics/settings.html
 9 #     https://docs.scrapy.org/en/latest/topics/downloader-middleware.html
10 #     https://docs.scrapy.org/en/latest/topics/spider-middleware.html
11 
12 BOT_NAME = 'scrapyDemo'
13 
14 SPIDER_MODULES = ['scrapyDemo.spiders']
15 NEWSPIDER_MODULE = 'scrapyDemo.spiders'
16 
17 
18 # Crawl responsibly by identifying yourself (and your website) on the user-agent
19 #USER_AGENT = 'scrapyDemo (+http://www.yourdomain.com)'
20 
21 # Obey robots.txt rules
22 ROBOTSTXT_OBEY = True
23 
24 # Configure maximum concurrent requests performed by Scrapy (default: 16)
25 #CONCURRENT_REQUESTS = 32
26 
27 # Configure a delay for requests for the same website (default: 0)
28 # See https://docs.scrapy.org/en/latest/topics/settings.html#download-delay
29 # See also autothrottle settings and docs
30 #DOWNLOAD_DELAY = 3
31 # The download delay setting will honor only one of:
32 #CONCURRENT_REQUESTS_PER_DOMAIN = 16
33 #CONCURRENT_REQUESTS_PER_IP = 16
34 
35 # Disable cookies (enabled by default)
36 #COOKIES_ENABLED = False
37 
38 # Disable Telnet Console (enabled by default)
39 #TELNETCONSOLE_ENABLED = False
40 
41 # Override the default request headers:
42 #DEFAULT_REQUEST_HEADERS = {
43 #   'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
44 #   'Accept-Language': 'en',
45 #}
46 
47 # Enable or disable spider middlewares
48 # See https://docs.scrapy.org/en/latest/topics/spider-middleware.html
49 #SPIDER_MIDDLEWARES = {
50 #    'scrapyDemo.middlewares.ScrapydemoSpiderMiddleware': 543,
51 #}
52 
53 # Enable or disable downloader middlewares
54 # See https://docs.scrapy.org/en/latest/topics/downloader-middleware.html
55 #DOWNLOADER_MIDDLEWARES = {
56 #    'scrapyDemo.middlewares.ScrapydemoDownloaderMiddleware': 543,
57 #}
58 
59 # Enable or disable extensions
60 # See https://docs.scrapy.org/en/latest/topics/extensions.html
61 #EXTENSIONS = {
62 #    'scrapy.extensions.telnet.TelnetConsole': None,
63 #}
64 
65 # Configure item pipelines
66 # See https://docs.scrapy.org/en/latest/topics/item-pipeline.html
67 #ITEM_PIPELINES = {
68 #    'scrapyDemo.pipelines.ScrapydemoPipeline': 300,
69 #}
70 
71 # Enable and configure the AutoThrottle extension (disabled by default)
72 # See https://docs.scrapy.org/en/latest/topics/autothrottle.html
73 #AUTOTHROTTLE_ENABLED = True
74 # The initial download delay
75 #AUTOTHROTTLE_START_DELAY = 5
76 # The maximum download delay to be set in case of high latencies
77 #AUTOTHROTTLE_MAX_DELAY = 60
78 # The average number of requests Scrapy should be sending in parallel to
79 # each remote server
80 #AUTOTHROTTLE_TARGET_CONCURRENCY = 1.0
81 # Enable showing throttling stats for every response received:
82 #AUTOTHROTTLE_DEBUG = False
83 
84 # Enable and configure HTTP caching (disabled by default)
85 # See https://docs.scrapy.org/en/latest/topics/downloader-middleware.html#httpcache-middleware-settings
86 #HTTPCACHE_ENABLED = True
87 #HTTPCACHE_EXPIRATION_SECS = 0
88 #HTTPCACHE_DIR = 'httpcache'
89 #HTTPCACHE_IGNORE_HTTP_CODES = []
90 #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。

 

很遗憾的说，推酷将在这个月底关闭。人生海海，几度秋凉，感谢那些有你的时光。