python Scrapy 從零開始學習筆記（一）

在之前我做了一個系列的關於 python 爬蟲的文章，傳送門：https://www.cnblogs.com/weijiutao/p/10735455.html，並寫了幾個爬取相關網站並提取有效信息的案例：https://www.cnblogs.com/weijiutao/p/10614694.html 等，從本章開始本人將繼續深入學習 python 爬蟲，主要是基於 Scrapy 庫展開，特此記錄，與君共勉！

Scrapy 官方網址：https://docs.scrapy.org/en/latest/

Scrapy 中文網址：https://scrapy-chs.readthedocs.io/zh_CN/latest/index.html

Scrapy 框架

• Scrapy是用純Python實現一個為了爬取網站數據、提取結構性數據而編寫的應用框架，用途非常廣泛。

• 框架的力量，用戶只需要定制開發幾個模塊就可以輕松的實現一個爬蟲，用來抓取網頁內容以及各種圖片，非常之方便。

• Scrapy 使用了 Twisted['twɪstɪd](其主要對手是Tornado)異步網絡框架來處理網絡通訊，可以加快我們的下載速度，不用自己去實現異步框架，並且包含了各種中間件接口，可以靈活的完成各種需求。

Scrapy架構圖(綠線是數據流向)：

 

• Scrapy Engine(引擎): 負責Spider、ItemPipeline、Downloader、Scheduler中間的通訊，信號、數據傳遞等。

• Scheduler(調度器): 它負責接受引擎發送過來的Request請求，並按照一定的方式進行整理排列，入隊，當引擎需要時，交還給引擎。

• Downloader（下載器）：負責下載Scrapy Engine(引擎)發送的所有Requests請求，並將其獲取到的Responses交還給Scrapy Engine(引擎)，由引擎交給Spider來處理，

• Spider（爬蟲）：它負責處理所有Responses,從中分析提取數據，獲取Item字段需要的數據，並將需要跟進的URL提交給引擎，再次進入Scheduler(調度器)，

• Item Pipeline(管道)：它負責處理Spider中獲取到的Item，並進行進行后期處理（詳細分析、過濾、存儲等）的地方.

• Downloader Middlewares（下載中間件）：你可以當作是一個可以自定義擴展下載功能的組件。

• Spider Middlewares（Spider中間件）：你可以理解為是一個可以自定擴展和操作引擎和Spider中間通信的功能組件（比如進入Spider的Responses;和從Spider出去的Requests）

以上是 Scrapy 的架構圖，從流程上看還是很清晰的，我就只簡單的說一下，首先從紅色方框的 Spider 開始，通過引擎發送給調度器任務，再將請求任務交給下載器並處理完后返回結果給 Spider，最后將結果交給關到來處理我們的結果就可以了。

上面的話可能還是會有些拗口，在接下來我們會一點點進行剖析，最后會發現利用 Scrapy 框架來做爬蟲是如此簡單。

Scrapy的安裝

windows 安裝  pip install scrapy 

Mac 安裝  sudo pip install scrapy 

pip 升級  pip install --upgrade pip 

本人目前使用的是Mac電腦，目前使用的是 python3 版本，內容上其實都大同小異，如遇系統或版本問題可及時聯系，互相學習！

安裝完成后我們在終端輸出 Scrapy 即可安裝是否成功：

 

新建項目

在 Scrapy 安裝成功之后，我們就需要用它來開發我們的爬蟲項目了，進入自定義的項目目錄中，運行下列命令：

 scrapy startproject spiderDemo 

運行上面的命令行就會在我們項目目錄下生成一下目錄結構：

 

 下面來簡單介紹一下各個主要文件的作用：

scrapy.cfg ：項目的配置文件

scrapyDemo/ ：項目的Python模塊，將會從這里引用代碼

scrapyDemo/items.py ：項目的目標文件

scrapyDemo/middlewares.py ：項目的中間件文件

scrapyDemo/pipelines.py ：項目的管道文件

scrapyDemo/settings.py ：項目的設置文件

scrapyDemo/spiders/ ：存儲爬蟲代碼目錄

 

接下來我們對各文件里的內容簡單說一下，里面的代碼目前都是最簡單的基本代碼，在接下來做案例的時候我們會再有針對地對文件做一下解釋。

 

其中的 __init_.py 文件內容都是空的，但是卻不能刪除掉，否則項目將無法啟動。

 

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

該文件是用來定義我們通過爬蟲所獲取到的有用的信息，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)

該文件為中間件文件，名字后面的s表示復數，說明這個文件里面可以放很多個中間件，我們用到的中間件可以在此定義

 

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

該文件俗稱管道文件，是用來獲取到我們的Item數據，並對數據做針對性的處理。

 

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'

該文件為我們的設置文件，一些基本的設置需要我們在此文件中進行配置，如我們的中間件文件當中的兩個類 ScrapydemoSpiderMiddleware，ScrapydemoDownloaderMiddleware 在 settings.py 中就能找到。

在 settings 文件中，我們常會配置到如上面的字段 如：ITEM_PIPELINES（管道文件），DEFAULT_REQUEST_HEADERS（請求報頭），DOWNLOAD_DELAY（下載延遲）

，ROBOTSTXT_OBEY（是否遵循爬蟲協議）等。

 

本章我們就先簡單的介紹一下 scrapy 的基本目錄，下一章我們來根據 scrapy 框架實現一個爬蟲案例。