When deploying web scrapers, it's important to respect the website's terms of service and the legal constraints regarding scraping. Assuming you are scraping in an ethical and legal manner, here are some best practices to prevent your web scraper from being blocked:
1. Follow robots.txt
The robots.txt file on a website gives instructions about which parts of the site should not be accessed by crawlers. Respect these rules to avoid legal issues and blocking.
2. Use Headers
Include a User-Agent string in your headers to identify your scraper as a legitimate bot. Some websites block requests without a User-Agent string or those that use a default one provided by scraping tools.
import requests
headers = {
'User-Agent': 'My Web Scraper 1.0',
}
response = requests.get('http://example.com', headers=headers)
3. Make Requests at Reasonable Intervals
Space out your requests to avoid hammering the server with too many requests in a short time. Use sleep or delay functions in your code.
import time
import requests
def scrape():
# ... your scraping logic here ...
time.sleep(10) # sleep for 10 seconds between requests
while True:
scrape()
4. Rotate IP Addresses
Use a pool of IP addresses to avoid getting blocked by IP-based rate-limiting. Proxy services can help with this.
import requests
proxies = [
'http://10.10.1.10:3128',
'http://11.11.1.11:3128',
# ... more proxies
]
for proxy in proxies:
try:
response = requests.get('http://example.com', proxies={"http": proxy})
# ... process the response ...
except requests.exceptions.ProxyError:
# ... handle proxy error ...
5. Rotate User Agents
Switch between different User-Agent strings to avoid detection.
import requests
import random
user_agents = [
'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3',
'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_5) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.1.1 Safari/605.1.15',
# ... more user agents
]
headers = {
'User-Agent': random.choice(user_agents),
}
response = requests.get('http://example.com', headers=headers)
6. Handle Errors Gracefully
Be prepared to handle HTTP errors like 429 (Too Many Requests), 4XX (Client Errors), and 5XX (Server Errors) gracefully. Implement retries with exponential backoff.
import requests
from requests.adapters import HTTPAdapter
from requests.packages.urllib3.util.retry import Retry
retry_strategy = Retry(
total=3,
status_forcelist=[429, 500, 502, 503, 504],
method_whitelist=["HEAD", "GET", "OPTIONS"],
backoff_factor=1
)
adapter = HTTPAdapter(max_retries=retry_strategy)
http = requests.Session()
http.mount("https://", adapter)
http.mount("http://", adapter)
response = http.get('http://example.com')
7. Use Headless Browsers Sparingly
Headless browsers like Puppeteer or Selenium are very powerful but also easy to detect. Use them only when necessary, and consider using techniques to make them look more like regular browsers.
8. Limit Concurrent Requests
Too many concurrent requests from the same IP can lead to blocking. Limit the number of concurrent requests and use a queue system if needed.
9. Respect the Website's Structure
Don't scrape at a pace faster than a human could possibly browse, and try to mimic human navigation patterns when possible.
10. Avoid Scraping During Peak Hours
Scraping during off-peak hours can be less noticeable and reduce the chance of being blocked.
11. Use Caching
Cache responses when possible to reduce the number of requests needed.
12. Monitor Your Activity
Keep an eye on your scraper's behavior and the website's responses. If you start receiving captchas or blocks, adjust your strategy.
Remember: Always check the website's terms of service and the legal aspects surrounding web scraping for the data you are accessing. Ethical scraping practices ensure that your activities respect the website owner's rights and help maintain an open and respectful web ecosystem.
