How Is a Web Crawler Used with Python?

The worldwide e-commerce sales from last year alone were $4.88 trillion, which is projected to keep rising.

This means that retail is growing exponentially, with more people looking to purchase online.

This provides an avenue for smaller businesses to compete and gather customers from every part of the globe, but you need data to do this.

Data collection doesn’t have to be a very complex task. It can be a simple exercise performed using simple tools. One of the best ways to build a simple web crawling tool is by using the Python programming language.

In the following sections, we will discuss what a web crawler is and how you can build one using the most straightforward language in the world. But, before that, this link explains what crawlers and crawling are in more detail, so do check it out if you’re interested in digging deeper into the topic.

Definition of Web Crawler

A web crawler works with a web scraper to harvest and collect data from multiple sources. A crawler is a small tool that initiates the process of data gathering through web crawling.

This first step involves going through links and finding more links with related content. The information from all the links and pages visited is collected and stored in a structured format.

The first link is generally called the seed link, while the others are called visited links. This has to happen for web scraping to occur more smoothly and can help guide the entire process of data collection.

It also ensures the data harvest is high-quality and relevant to the subject of discussion. Businesses use web crawlers to collect data for many different reasons, as we will see shortly.

Major Use Cases of a Web Crawler

Web crawlers have several uses as they demonstrate a wide array of functionality. Below are some of the major use cases:

  1. Indexing Content

All new websites need to be indexed on search engines. This is because it is the only way to be displayed in search results.

Indexing is also constantly done for old websites that update their content regularly.

Search engine crawling bots are used to navigate through web pages and collect their content regularly.

  1. Checking Vulnerabilities

Website vulnerabilities are a real thing. They are issues that can make a website perform less than expected.

One such issue could be poor response or loading time. Website developers use web crawlers to crawl their websites to repeatedly catch these issues before deployment.

  1. Optimizing Websites

Crawlers can also be used to improve search engine optimization (SEO). Each website and page often start at the bottom of the ranking, and to improve ranking, some things have to be done.

These things include adding excellent keywords and backlinks that point to relevant content. Web crawlers are used to crawl the internet to find both keywords and relevant links, which are then used to optimize both the site and its content.

How to Build a Web Crawler from Scratch in Python

Now that you have a better grasp of what is a web crawler and some of the things it can do, let us look at how you can build one from the ground up using the Python language.

A typical Python crawling spider should perform two jobs at once. First, it needs to be able to grab and extract HTML files. Next, it needs to have the capacity to parse and extract links from the HTML file.

Building this machine is simple, especially since Python scripts are only written with a few lines of good syntaxes.

To build the first part of making requests and extracting HTML files, you can use the standard library Urllib to build the parser, and you can use the library HTML Parser. And you can follow this example to see how to get it done.

Why Using an Existing Reliable Crawler Can Be Useful As Well

Building the script described above is easy, and anyone with a little programming language can get it done.

However, the bot itself might be slower than you might want. It may also display no true parallelism. The bot could send out a request to a URL, and it has to wait for the request to be resolved without doing anything else while it waits.

Moreover, the crawling only works for a small number of URLs as large scale crawling is impractical.

Lastly, the bot never identifies itself to the website and server as a proper crawler. This breaks and violates any robots.txt rules existing on the website.

These disadvantages are piled on top of the time and energy that you will expend building something that barely works.

This is why using an existing reliable crawler built and managed by a third-party firm is always an alternative.

Not only does it save you the time and energy that you can easily use for other things, but it also delivers a proper crawler to you.


If you now understand that data is important, your next quest should be finding the right tools to get this data.And when you choose to use a web crawler, you could either choose to build it yourself using Python. Or you could opt for a ready-made crawling script.

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