# Web Scraping

Web scraping, also known as *web data extraction* or *web harvesting*, is the process of extracting data from web pages. It involves making HTTP requests to web pages, downloading their front-facing code, and then parsing this code in order to extract the desired information. This process can be done manually, but there are many tools available that help automate it.

## How Does Web Scraping Work?

Here is a simple breakdown of the web scraping process:

1. **Request** - An HTTP request is made to the target website.
2. **Response** - The website responds with its containing content: HTML, CSS, JavaScript, images, etc.
3. **Parse** - Tools are then used to process the content returned from the webpage. Many different techniques can be used here. Regular expressions, webpage structuring attributes (div, table, etc.), parsing libraries, etc. are all examples of strategies used to locate and extract the desired data.
4. **Application** - The extracted data is then analyzed/used for the desired purpose.

## Why is Web Scraping Useful?

### 1. Data Collection

The most prominent application of web scraping is data collection. A few beneficial examples:

- **Research** - Academic researchers might scrape websites to gather data for their studies.
- **Statistics** - Analysts might scrape large, sweeping data sources for studying general trends or opinions.
- **Market Analysis** - Businesses might scrape e-commerce websites to monitor competitor prices and product offerings.
- **Price Comparison** - Businesses or individuals might scrape various sources to compare competing prices.
- **News Aggregation** - Individuals or outlets might scrape various news websites to create an aggregated view on issues.

### 2. Automation

Web scraping can be used to automate repetitive tasks. This can save lots of time. A few beneficial examples:

- Aggregating content from sources into a usable format.
- Retrieving item ratings in order to sort and analyze them.
- Checking stock levels of products across various online stores.
- Gathering real estate listings from multiple websites for comparison.

### 3. Monitoring

Web scraping can be used to monitor changes on web pages in real-time, beneficial for:

- Automated event monitoring, like tickets going on sale.
- Checking prices at defined intervals to check for deals and special offerings.
- Checking inventory of an item that frequently goes out of stock
- Finding and responding to job alerts as quickly as possible.
- Availability of products/services.
- Monitoring website updates or changes.
- Automated update notifications.

### 4. Integration

Web scraping can bridge the gap when a website doesn't offer an official API. Once the data is scraped from the website, it can be integrated into other systems or applications (just like an API would have done).

## Important Considerations

Web scraping can be incredibly valuable, but it's crucial to be aware of its limitations and legal/ethical considerations:

- **Legal Considerations** - Not all websites allow web scraping. Always check a website's policies before performing any scraping. Most websites will have a `robots.txt` file which describes their terms of service. In addition, scraping too frequently can be seen as a denial-of-service attack, which is illegal.
- **Ethical Considerations** - Some websites simply do not have the server bandwidth to accomodate your scraping AND provide a performant experience to other end-users. This can be inconsiderate and taxing on the website owners. Always consider the effects you are having on the people running the website and your fellow users.
- **Limitations** - Websites change their structure often which can break your scraping scripts. Additionally, some websites use security mechanisms like CAPTCHAs to prevent automated access.
