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Introduction to web scraping

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Conclusion

Overview

Teaching: 15 min
Exercises: 15 min
Questions

  • When is web scraping OK and when is it not?

  • Is web scraping legal? Can I get into trouble?

  • How can I make sure I’m doing the right thing?

  • What can I do with the data that I’ve scraped?

Objectives

  • Wrap things up

  • Discuss the legal implications of web scraping

  • Establish a code of conduct

Now that we have seen several different ways to scrape data from websites and are ready to start working on potentially larger projects, we may ask ourselves whether there are any legal implications of writing a piece of computer code that downloads information from the Internet.

In this section, we will be discussing some of the issues to be aware of when scraping websites, and we will establish a code of conduct (below) to guide our web scraping projects.

Please note that the information provided on this page is for information purposes only and does not constitute professional legal advice on the practice of web scraping.

If you are concerned about the legal implications of using web scraping on a project you are working on, it is probably a good idea to seek advice from a professional, preferably someone who has knowledge of the intellectual property (copyright) legislation in effect in your country.

Don’t break the web: Denial of Service attacks

The first and most important thing to be careful about when writing a web scraper is that it typically involves querying a website repeatedly and accessing a potentially large number of pages. For each of these pages, a request will be sent to the web server that is hosting the site, and the server will have to process the request and send a response back to the computer that is running our code. Each of these requests will consume resources on the server, during which it will not be doing something else, like for example responding to someone else trying to access the same site.

If we send too many such requests over a short span of time, we can prevent other “normal” users from accessing the site during that time, or even cause the server to run out of resources and crash.

In fact, this is such an efficient way to disrupt a web site that hackers are often doing it on purpose. This is called a Denial of Service (DoS) attack.

Since DoS attacks are unfortunately a common occurence on the Internet, modern web servers include measures to ward off such illegitimate use of their resources. They are watchful for large amounts of requests appearing to come from a single computer or IP address, and their first line of defense often involves refusing any further requests coming from this IP address.

A web scraper, even one with legitimate purposes and no intent to bring a website down, can exhibit similar behaviour and, if we are not careful, result in our computer being banned from accessing a website.

The good news is that a good web scraper, such as Scrapy, recognizes that this is a risk and includes measures to prevent our code from appearing to launch a DoS attack on a website. This is mostly done by inserting a random delay between individual requests, which gives the target server enough time to handle requests from other users between ours.

This is Scrapy’s default behaviour, and it should prevent most scraping projects from ever causing problems. To be on the safe side, however, it is good practice to limit the number of pages we are scraping while we are still writing and debugging our code. This is why in the previous section, we imposed a limit of five pages to be scraped, which we only removed when we were reasonably certain the scraper was working as it should.

Limiting requests to a particular domain, by using Scrapy’s allowed_domains property is another way to make sure our code is not going to start scraping the entire Internet by mistake.

Thanks to the defenses web servers use to protect themselves against DoS attacks and Scrapy’s measure to avoid inadvertently launching such an attack, the risks of causing trouble is limited.

It is important to recognize that in certain circumstances web scraping can be illegal. If the terms and conditions of the web site we are scraping specifically prohibit downloading and copying its content, then we could be in trouble for scraping it.

In practice, however, web scraping is a tolerated practice, provided reasonable care is taken not to disrupt the “regular” use of a web site, as we have seen above.

In a sense, web scraping is no different than using a web browser to visit a web page, in that it amounts to using computer software (a browser vs a scraper) to acccess data that is publicly available on the web.

In general, if data is publicly available (the content that is being scraped is not behind a password-protected authentication system), then it is OK to scrape it, provided we don’t break the web site doing so. What is potentially problematic is if the scraped data will be shared further. For example, downloading content off one website and posting it on another website (as our own), unless explicitely permitted, would constitute copyright violation and be illegal.

However, most copyright legislations recognize cases in which reusing some, possibly copyrighted, information in an aggregate or derivative format is considered “fair use”. In general, unless the intent is to pass off data as our own, copy it word for word or trying to make money out of it, reusing publicly available content scraped off the internet is OK.

Better be safe than sorry

Be aware that copyright and data privacy legislation typically differs from country to country. Be sure to check the laws that apply in your context. For example, in Australia, it can be illegal to scrape and store personal information such as names, phone numbers and email addresses, even if they are publicly available.

If you are looking to scrape data for your own personal use, then the above guidelines should probably be all that you need to worry about. However, if you plan to start harvesting a large amount of data for research or commercial purposes, you should probably seek legal advice first.

If you work in a university, chances are it has a copyright office that will help you sort out the legal aspects of your project. The university library is often the best place to start looking for help on copyright.

Be nice: ask and share

Depending on the scope of your project, it might be worthwhile to consider asking the owners or curators of the data you are planning to scrape if they have it already available in a structured format that could suit your project. If your aim is do use their data for research, or to use it in a way that could potentially interest them, not only it could save you the trouble of writing a web scraper, but it could also help clarify straight away what you can and cannot do with the data.

On the other hand, when you are publishing your own data, as part of a research project, documentation or a public website, you might want to think about whether someone might be interested in getting your data for their own project. If you can, try to provide others with a way to download your raw data in a structured format, and thus save them the trouble to try and scrape your own pages!

Web scraping code of conduct

This all being said, if you adhere to the following simple rules, you will probably be fine.

  1. Ask nicely. If your project requires data from a particular organisation, for example, you can try asking them directly if they could provide you what you are looking for. With some luck, they will have the primary data that they used on their website in a structured format, saving you the trouble.
  2. Don’t download copies of documents that are clearly not public. For example, academic journal publishers often have very strict rules about what you can and what you cannot do with their databases. Mass downloading article PDFs is probably prohibited and can put you (or at the very least your friendly university librarian) in trouble. If your project requires local copies of documents (e.g. for text mining projects), special agreements can be reached with the publisher. The library is a good place to start investigating something like that.
  3. Check your local legislation. For example, certain countries have laws protecting personal information such as email addresses and phone numbers. Scraping such information, even from publicly avaialable web sites, can be illegal (e.g. in Australia).
  4. Don’t share downloaded content illegally. Scraping for personal purposes is usually OK, even if it is copyrighted information, as it could fall under the fair use provision of the intellectual property legislation. However, sharing data for which you don’t hold the right to share is illegal.
  5. Share what you can. If the data you scraped is in the public domain or you got permission to share it, then put it out there for other people to reuse it (e.g. on datahub.io). If you wrote a web scraper to access it, share its code (e.g. on GitHub) so that others can benefit from it.
  6. Don’t break the Internet. Not all web sites are designed to withstand thousands of requests per second. If you are writing a recursive scraper (i.e. that follows hyperlinks), test it on a smaller dataset first to make sure it does what it is supposed to do. Adjust the settings of your scraper to allow for a delay between requests. By default, Scrapy uses conservative settings that should minimize this risk.
  7. Publish your own data in a reusable way. Don’t force others to write their own scrapers to get at your data. Use open and software-agnostic formats (e.g. JSON, XML), provide metadata (data about your data: where it came from, what it represents, how to use it, etc.) and make sure it can be indexed by search engines so that people can find it.

Going further

This lesson only provides an introduction to the practice of web scraping and highlights some of the tools available. Scrapy has many more features than those mentioned in the previous section, be sure to refer to its full documentation for details.

Happy scraping!

References

Key Points

  • Web scraping is, in general, legal and won’t get you into trouble.

  • There are a few things to be careful about, notably don’t overwhelm a web server and don’t steal content.

  • Be nice. In doubt, ask.

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