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Web Scraping with PythonScrape data from any website with the power of PythonRichard LawsonBIRMINGHAM - MUMBAI

Web Scraping with PythonCopyright 2015 Packt PublishingAll rights reserved. No part of this book may be reproduced, stored in a retrievalsystem, or transmitted in any form or by any means, without the prior writtenpermission of the publisher, except in the case of brief quotations embedded incritical articles or reviews.Every effort has been made in the preparation of this book to ensure the accuracyof the information presented. However, the information contained in this book issold without warranty, either express or implied. Neither the author, nor PacktPublishing, and its dealers and distributors will be held liable for any damagescaused or alleged to be caused directly or indirectly by this book.Packt Publishing has endeavored to provide trademark information about all of thecompanies and products mentioned in this book by the appropriate use of capitals.However, Packt Publishing cannot guarantee the accuracy of this information.First published: October 2015Production reference: 1231015Published by Packt Publishing Ltd.Livery Place35 Livery StreetBirmingham B3 2PB, UK.ISBN 978-1-78216-436-4www.packtpub.com

CreditsAuthorRichard LawsonReviewersMartin BurchProject CoordinatorMilton DsouzaProofreaderSafis EditingChristopher DavisWilliam SankeyAyush TiwariAcquisition EditorRebecca YouéContent Development EditorAkashdeep KunduTechnical EditorsNovina KewalramaniShruti RawoolCopy EditorSonia CheemaIndexerMariammal ChettiarProduction CoordinatorNilesh R. MohiteCover WorkNilesh R. Mohite

About the AuthorRichard Lawson is from Australia and studied Computer Science at the Universityof Melbourne. Since graduating, he built a business specializing at web scrapingwhile traveling the world, working remotely from over 50 countries. He is afluent Esperanto speaker, conversational at Mandarin and Korean, and active incontributing to and translating open source software. He is currently undertakingpostgraduate studies at Oxford University and in his spare time enjoys developingautonomous drones.I would like to thank Professor Timothy Baldwin for introducing meto this exciting field and Tharavy Douc for hosting me in Paris whileI wrote this book.

About the ReviewersMartin Burch is a data journalist based in New York City, where he makesinteractive graphics for The Wall Street Journal. He holds a master of arts injournalism from the City University of New York's Graduate School of Journalism,and has a baccalaureate from New Mexico State University, where he studiedjournalism and information systems.I would like to thank my wife, Lisa, who encouraged me to assistwith this book; my uncle, Michael, who has always patientlyanswered my programming questions; and my father, Richard, whoinspired my love of journalism and writing.William Sankey is a data professional and hobbyist developer who lives inCollege Park, Maryland. He graduated in 2012 from Johns Hopkins Universitywith a master's degree in public policy and specializes in quantitative analysis. Heis currently a health services researcher at L&M Policy Research, LLC, working onprojects for the Centers for Medicare and Medicaid Services (CMS). The scope ofthese projects range from evaluating Accountable Care Organizations to monitoringthe Inpatient Psychiatric Facility Prospective Payment System.I would like to thank my devoted wife, Julia, and rambunctiouspuppy, Ruby, for all their love and support.

Ayush Tiwari is a Python developer and undergraduate at IIT Roorkee. He hasbeen working at Information Management Group, IIT Roorkee, since 2013, and hasbeen actively working in the web development field. Reviewing this book has been agreat experience for him. He did his part not only as a reviewer, but also as an avidlearner of web scraping. He recommends this book to all Python enthusiasts so thatthey can enjoy the benefits of scraping.He is enthusiastic about Python web scraping and has worked on projects such as livesports feeds, as well as a generalized Python e-commerce web scraper (at Miranj).He has also been handling a placement portal with the help of a Django app to assistthe placement process at IIT Roorkee.Besides backend development, he loves to work on computational Python/dataanalysis using Python libraries, such as NumPy, SciPy, and is currently workingin the CFD research field. You can visit his projects on GitHub. His usernameis tiwariayush.He loves trekking through Himalayan valleys and participates in several treksevery year, adding this to his list of interests, besides playing the guitar. Among hisaccomplishments, he is a part of the internationally acclaimed Super 30 group andhas also been a rank holder in it. When he was in high school, he also qualified forthe International Mathematical Olympiad.I have been provided a lot of help by my family members (my sister, Aditi, myparents, and Anand sir), my friends at VI and IMG, and my professors. I would liketo thank all of them for the support they have given me.Last but not least, kudos to the respected author and the Packt Publishing teamfor publishing these fantastic tech books. I commend all the hard work involved inproducing their books.

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Table of ContentsPrefaceChapter 1: Introduction to Web ScrapingWhen is web scraping useful?Is web scraping legal?Background researchChecking robots.txtExamining the SitemapEstimating the size of a websiteIdentifying the technology used by a websiteFinding the owner of a websiteCrawling your first websiteDownloading a web pageRetrying downloadsSetting a user agentSitemap crawlerID iteration crawlerLink crawlerv11223446678810111114Advanced features16Summary20Chapter 2: Scraping the DataAnalyzing a web pageThree approaches to scrape a web pageRegular expressionsBeautiful SoupLxmlCSS selectors[i]21222424262728

Table of ContentsComparing performance29Scraping resultsOverviewAdding a scrape callback to the link crawlerSummary30323234Chapter 3: Caching Downloads35Chapter 4: Concurrent Downloading49Chapter 5: Dynamic Content61Adding cache support to the link crawlerDisk cacheImplementationTesting the cacheSaving disk spaceExpiring stale dataDrawbacksDatabase cacheWhat is NoSQL?Installing MongoDBOverview of MongoDBMongoDB cache implementationCompressionTesting the cacheSummaryOne million web pagesParsing the Alexa listSequential crawlerThreaded crawlerHow threads and processes workImplementationCross-process crawlerPerformanceSummaryAn example dynamic web pageReverse engineering a dynamic web pageEdge casesRendering a dynamic web pagePyQt or PySideExecuting JavaScript[ ii 26467696970

Table of ContentsWebsite interaction with WebKit72Waiting for resultsThe Render class7374SeleniumSummary7678Chapter 6: Interacting with Forms79Chapter 7: Solving CAPTCHA93The Login formLoading cookies from the web browserExtending the login script to update contentAutomating forms with the Mechanize moduleSummary8083879091Registering an accountLoading the CAPTCHA imageOptical Character RecognitionFurther improvementsSolving complex CAPTCHAsUsing a CAPTCHA solving serviceGetting started with 9kw949596100100101102Integrating with registrationSummary1081099kw CAPTCHA API103Chapter 8: Scrapy111InstallationStarting a projectDefining a modelCreating a spider111112113114Tuning settingsTesting the spider115116Scraping with the shell commandChecking resultsInterrupting and resuming a crawlVisual scraping with PortiaInstallationAnnotationTuning a spiderChecking resultsAutomated scraping with ScrapelySummary117118121122122124127129130131[ iii ]

Table of ContentsChapter 9: Overview133Index147Google search engineFacebookThe websiteThe APIGapBMWSummary133137138139140142146[ iv ]

PrefaceThe Internet contains the most useful set of data ever assembled, which is largelypublicly accessible for free. However, this data is not easily reusable. It is embeddedwithin the structure and style of websites and needs to be extracted to be useful.This process of extracting data from web pages is known as web scraping and isbecoming increasingly useful as ever more information is available online.What this book coversChapter 1, Introduction to Web Scraping, introduces web scraping and explains ways tocrawl a website.Chapter 2, Scraping the Data, shows you how to extract data from web pages.Chapter 3, Caching Downloads, teaches you how to avoid redownloading bycaching results.Chapter 4, Concurrent Downloading, helps you to scrape data faster by downloadingin parallel.Chapter 5, Dynamic Content, shows you how to extract data from dynamic websites.Chapter 6, Interacting with Forms, shows you how to work with forms to access thedata you are after.Chapter 7, Solving CAPTCHA, elaborates how to access data that is protected byCAPTCHA images.[v]

PrefaceChapter 8, Scrapy, teaches you how to use the popular high-level Scrapy framework.Chapter 9, Overview, is an overview of web scraping techniques that have been covered.What you need for this bookAll the code used in this book has been tested with Python 2.7, and is available fordownload at http://bitbucket.org/wswp/code. Ideally, in a future version ofthis book, the examples will be ported to Python 3. However, for now, many ofthe libraries required (such as Scrapy/Twisted, Mechanize, and Ghost) are onlyavailable for Python 2. To help illustrate the crawling examples, we created a samplewebsite at http://example.webscraping.com. This website limits how fast youcan download content, so if you prefer to host this yourself the source code andinstallation instructions are available at http://bitbucket.org/wswp/places.We decided to build a custom website for many of the examples used in this bookinstead of scraping live websites, so that we have full control over the environment.This provides us stability—live websites are updated more often than books, and bythe time you try a scraping example, it may no longer work. Also, a custom websiteallows us to craft examples that illustrate specific skills and avoid distractions. Finally,a live website might not appreciate us using them to learn about web scraping and tryto block our scrapers. Using our own custom website avoids these risks; however, theskills learnt in these examples can certainly still be applied to live websites.Who this book is forThis book requires prior programming experience and would not be suitable forabsolute beginners. When practical we will implement our own version of webscraping techniques so that you understand how they work before introducing thepopular existing module. These examples will assume competence with Python andinstalling modules with pip. If you need a brush up, there is an excellent free onlinebook by Mark Pilgrim available at http://www.diveintopython.net. This is theresource I originally used to learn Python.The examples also assume knowledge of how web pages are constructed with HTMLand updated with JavaScript. Prior knowledge of HTTP, CSS, AJAX, WebKit, andMongoDB would also be useful, but not required, and will be introduced as andwhen each technology is needed. Detailed references for many of these topics areavailable at http://www.w3schools.com.[ vi ]

PrefaceConventionsIn this book, you will find a number of styles of text that distinguish betweendifferent kinds of information. Here are some examples of these styles, and anexplanation of their meaning.Code words in text are shown as follows: "Most websites define a robots.txt file tolet robots know any restrictions about crawling their website."A block of code is set as follows: ?xml version "1.0" encoding "UTF-8"? urlset xmlns "http://www.sitemaps.org/schemas/sitemap/0.9" url loc http://example.webscraping.com/view/Afghanistan-1 /loc /url url loc 2 /loc /url url loc http://example.webscraping.com/view/Albania-3 /loc /url . /urlset When we wish to draw your attention to a particular part of a code block, therelevant lines or items are set in bold:def link crawler(., scrape callback None): links []if scrape callback:links.extend(scrape callback(url, html) or []).Any command-line input or output is written as follows: python performance.pyRegular expressions: 5.50 secondsBeautifulSoup: 42.84 secondsLxml: 7.06 seconds[ vii ]

PrefaceNew terms and important words are shown in bold. Words that you see on thescreen, in menus or dialog boxes for example, appear in the text like this: " Whenregular users open this web page in their browser, they will enter their e-mail andpassword, and click on the Log In button to submit the details to the server."Warnings or important notes appear in a box like this.Tips and tricks appear like this.Reader feedbackFeedback from our readers is always welcome. Let us know what you think aboutthis book—what you liked or may have disliked. Reader feedback is important for usto develop titles that you really get the most out of.To send us general feedback, simply send an e-mail to feedback@packtpub.com,and mention the book title through the subject of your message.If there is a topic that you have expertise in and you are interested in either writingor contributing to a book, see our author guide on www.packtpub.com/authors.Customer supportNow that you are the proud owner of a Packt book, we have a number of things tohelp you to get the most from your purchase.ErrataAlthough we have taken every care to ensure the accuracy of our content, mistakesdo happen. If you find a mistake in one of our books—maybe a mistake in the text orthe code—we would be grateful if you would report this to us. By doing so, you cansave other readers from frustration and help us improve subsequent versions of thisbook. If you find any errata, please report them by visiting http://www.packtpub.com/support, selecting your book, clicking on the errata submission form link, andentering the details of your errata. Once your errata are verified, your submissionwill be accepted and the errata will be uploaded to our website, or added to any listof existing errata, under the Errata section of that title.[ viii ]

PrefacePiracyPiracy of copyright material on the Internet is an ongoing problem across all media.At Packt, we take the protection of our copyright and licenses very seriously. If youcome across any illegal copies of our works, in any form, on the Internet, pleaseprovide us with the location address or website name immediately so that we canpursue a remedy.Please contact us at copyright@packtpub.com with a link to the suspectedpirated material.We appreciate your help in protecting our authors, and our ability to bring youvaluable content.QuestionsYou can contact us at questions@packtpub.com if you are having a problem withany aspect of the book, and we will do our best to address it.[ ix ]

Introduction to Web ScrapingIn this chapter, we will cover the following topics: Introduce the field of web scraping Explain the legal challenges Perform background research on our target website Progressively building our own advanced web crawlerWhen is web scraping useful?Suppose I have a shop selling shoes and want to keep track of my competitor'sprices. I could go to my competitor's website each day to compare each shoe's pricewith my own, however this would take a lot of time and would not scale if I soldthousands of shoes or needed to check price changes more frequently. Or maybeI just want to buy a shoe when it is on sale. I could come back and check the shoewebsite each day until I get lucky, but the shoe I want might not be on sale formonths. Both of these repetitive manual processes could instead be replaced withan automated solution using the web scraping techniques covered in this book.In an ideal world, web scraping would not be necessary and each website wouldprovide an API to share their data in a structured format. Indeed, some websites doprovide APIs, but they are typically restricted by what data is available and howfrequently it can be accessed. Additionally, the main priority for a website developerwill always be to maintain the frontend interface over the backend API. In short, wecannot rely on APIs to access the online data we may want and therefore, need to learnabout web scraping techniques.[1]

Introduction to Web ScrapingIs web scraping legal?Web scraping is in the early Wild West stage, where what is permissible is still beingestablished. If the scraped data is being used for personal use, in practice, there isno problem. However, if the data is going to be republished, then the type of datascraped is important.Several court cases around the world have helped establish what is permissible whenscraping a website. In Feist Publications, Inc. v. Rural Telephone Service Co., the UnitedStates Supreme Court decided that scraping and republishing facts, such as telephonelistings, is allowed. Then, a similar case in Australia, Telstra Corporation Limited v. PhoneDirectories Company Pty Ltd, demonstrated that only data with an identifiable authorcan be copyrighted. Also, the European Union case, ofir.dk vs home.dk, concluded thatregular crawling and deep linking is permissible.These cases suggest that when the scraped data constitutes facts (such as businesslocations and telephone listings), it can be republished. However, if the data isoriginal (such as opinions and reviews), it most likely cannot be republished forcopyright reasons.In any case, when you are scraping data from a website, remember that you are theirguest and need to behave politely or they may ban your IP address or proceed withlegal action. This means that you should make download requests at a reasonablerate and define a user agent to identify you. The next section on crawling will coverthese practices in detail.You can read more about these legal cases at ourt US&vol 499&invol 340, .html, andhttp://www.bvhd.dk/uploads/tx mocarticles/S -og Handelsrettens afg relse i Ofir-sagen.pdf.Background researchBefore diving into crawling a website, we should develop an understanding aboutthe scale and structure of our target website. The website itself can help us throughtheir robots.txt and Sitemap files, and there are also external tools available toprovide further details such as Google Search and WHOIS.[2]

Chapter 1Checking robots.txtMost websites define a robots.txt file to let crawlers know of any restrictions aboutcrawling their website. These restrictions are just a suggestion but good web citizenswill follow them. The robots.txt file is a valuable resource to

learner of web scraping. He recommends this book to all Python enthusiasts so that they can enjoy the benefits of scraping. He is enthusiastic about Python web scraping and has worked on projects such as live sports feeds, as well as a generalized

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