XPath: How Python Parses HTML

3 min read

How Python HTML parser parse HTML data? The answer is: Xpath. Knowing what Xpath is and how it works is important to the accuracy of data extraction.

What is an HTML Parser

Most of websites are usually written in HTML and HTML documents consist of constructed elements with tags. Let’s put it this way. Generally, invalid HTML elements could be more common than valid ones. Why is so important to deal with invalid HTML? Because most of us need to grab useful information from enormous amounts of resources inside these HTML files, analyze the data we’ve extracted and then draw conclusions. We gain insight when we draw conclusions from the data and information we’ve collected. 

An HTML parser can make unstructured data more readable and comfortable. You can use an HTML parser to collect the information you wanted and save the information in data formats that are most useful to you. You can code such a parser that can easily locate any HTML elements by ID attribute, Name attribute, or any other tag type. Some HTML parser generators seem like good tools when you write your own parser. But sometimes the reported messages of certain generators are not so reliable and you may need to spend much more time and energy in resolving conflicts. It seems that the best solution to parse an HTML documents is to write a parser by hand. On the other hand, there are many useful HTML parsers that can solve most of the problems. You can choose one of them to best fit your different needs after considering many popular parsing tools. It greatly saves you invaluable time and effort. For example, a Python HTML parser is a module that converts HTML into XML and addresses parts of an XML document via XPath. Here, you need to know what XPath is and how it works.

What is XPath

XPath (the XML Path language), which is defined by the W3C, is a language for finding information in an XML document. 

  • XPath is a syntax for defining parts of an XML document.
  • XPath uses path expressions to navigate in XML documents.
  • XPath contains a library of standard functions.
  • XPath is a major element in XSLT.

XPath uses a compact, non-XML syntax and operates on the abstract, logical structure of an XML document, instead of its surface syntax. In fact, Xpath is used to define elements of an XML document and its Path expressions are used to select nodes or node-sets in XML documents. These path expressions look very much like the expressions you see when you work with a traditional computer file system. Today XPath expressions can also be used in JavaScript, Java, XML Schema, PHP, Python, C and C++, and lots of other languages. For more information about the W3C definition of the XPath, see XPath Toturial

Bulk Extract Data from HTML Documents

There‘re plenty of tutorials and examples of how to use XPath to navigate to elements in an HTML document. You need to try to learn how to get familiar with XPath syntax yourself by reading online materials and using an online XPath tester to test your expressions/queries many times. But, if you want to extract large amounts of data from simple websites like Amazon, LinkedIn, etc. in a short time, we’d recommend you to try out Octoparse.

As a powerful yet easy-to-use web data extraction tool, Octoparse is capable of parsing HTML web pages automatically. It simulates human browsing behavior to browse, login, enter texts, click content, and extract data you want. No coding knowledge required. It generates XPath automatically when you configure an extraction task to collect HTML elements and converts the data that you extracted into structured data formats like Excel, HTML, etc. Moreover, it provides cloud service to meet your web scraping needs. 

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