02-05-2021

Web Scraping W3schools



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CSS Selectors are very common in web data scraping using Agenty chrome extension. You can use the CSS selector to extract any content from the HTML pages. Selectors are the part of CSS rule set and select HTML elements according to its Id, class, type, attribute or pseudo-classes.

Web scraping, or web harvesting, is the term we use to describe the process of extracting data from a website. The reason we can do this is because the information used by a browser to render webpages is received as a text file from a server. Two examples are Codeacademy 83 and W3schools 84. 23.2 The rvest package. The tidyverse provides a. Web Scraper uses css selectors to find HTML elements in web pages and to extract data from them. When selecting an element the Web Scraper will try to make its best guess what the CSS selector might be for the selected elements. But you can also write it yourself and test it. Write a Python program to test if a given page is found or not on the server. Click me to see the. Web scraping, also called web data mining or web harvesting, is the process of constructing an agent which can extract, parse, download and organize useful information from the web automatically. This tutorial will teach you various concepts of web scraping and makes you comfortable with scraping various types of websites and their data.

The CSS selectors are easy to understand and quick to learn, you can use our chrome extension to generate CSS selectors automatically or can type manually to test the selectors and see the result preview.

Web sites don’t always provide their data in comfortable formats such as CSV or JSON. This is where web scraping comes in. Web scraping is the practice of using a computer program to sift through a web page and gather the data that you need in a format most useful to you while at the same time preserving the structure of the data.

In this tutorial, we will learn some basic CSS selectors and how to write them to extract the data from HTML pages. And you can find the complete reference here

We are going to using this HTML page with HTML source below. The page is hosted on github and open source to try CSS selectors using web scraping agent.

#id selector

The #id selector uses the _id _attribute of an HTML element to scrape a specific element. The id of an element is a unique identifier of particular HTML tag, so the id selector is used to select one unique element or all elements under the id.

To extract an element with a specific id write a hash (#) character followed by the id of the element in selector field. The difference between an id and a class is that an id can be used to identify one element whereas a c_lass_ can be used to identify many elements.

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Example :

The “I live in New York” extracted form this HTML example is extracted using the #myAddress selector.

.class selector

The _class_ selector scrape all the elements with a specific class attribute. A class to search for an element can have multiple classes. Only one of them must match and to select elements with a specific class write a period (.) character followed by the name of the class.

**Example **

As in above screenshot, Agenty scraped each matching element using .introduction in this HTML example. So we can use the class selectors to scrape data from HTML pages using .class selector.

* selector

The * selector scrape all the elements available on the page, and can extracts all elements.

Example

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As in the screenshot given above, Agenty extracted each item which is under the tag.

element selector

The element selector scrape all elements with the specified element name.

The td element defines standard cells in HTML table. Here we can see the data of the table extracted using the td element selector. So, we can use the name of element to extract any data from all the element of that type.

**Example **

As given in the above example, Agenty scraped all 8 td elements items containing from the table.

element, element selector

The element, element selector are used to scrape all elements that are placed immediately after (not inside) the first specified element.

You can specify any number of selectors to combine into a single result. This multiple expression combination is an efficient way to scrape multiple data-points into the single field. For example, using the th, td selector will scrape the text for both elements - table header and table rows.

We can add any number of elements(or selector) separated by commas to scrape multiple data points.

Example

element element selector

The element element selector are used to extract elements inside elements.

When we are extracting the data, which is present in a particular parent tag. We can write our selector using the parent tag to extract only the element having the parent name provided. For example, If I want to extract the 3 paragraphs under the div tag with introduction class. I can use the .introduction p selector which will match only the p which has the parent as .introduction and not any others.

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**Example **

element > element selector

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The element > element selector are used to scrape elements with a specific parent. But elements that are not directly a child of the specified parent, are not scraped.

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This selector is used to extract content with direct Parent > Child relationship. For example, using table > tbody > tr > th tells Agenty, that extracts all elements where the parent is a table > tbody > tr elements

Example