Web scraping, also known as web data extraction, can be a useful way to collect large amounts of data from websites. However, it does come with some risks that scrapers should be aware of.
Respecting Terms of Service
Many websites prohibit scraping in their terms of service or robots.txt file. Scraping these sites without permission could result in legal issues. Before scraping any site, carefully review their terms of service and robots.txt rules. If scraping is not allowed, consider requesting special access from the site owner.
Avoiding Overloading Servers
Scraping too aggressively can overload servers and get your IP address blocked. Use throttling, proxies and random time delays between requests to scrape responsibly. Spread out requests over multiple IP addresses and long time periods.
Preventing Data Corruption
Web pages are dynamic - content can update while you are scraping, leading to inconsistent data. Design scrapers to detect changes and handle them appropriately. For example, ignore cached/duplicate copies or scrape atomic blocks of related data using timestamps.
Masking Scraping Activities
Many sites try to detect and block scrapers. Use realistic headers, mimick human browsing patterns and monitor if you get blocked. Proxies, browser automation tools like Selenium and CAPTCHA solving services can mask scraping patterns.
The key is to scrape ethically - respect sites' wishes, scrape responsibly and invest in robust scraping code that handles errors and changes. With some care, web scraping can be done without harming sites or compromising data quality. Let the site owners know what you are doing and work with them if possible.