input: from typing import List
  
  def extract_web_data(website_url: str) -> List[str]:
      """Create a web scraper using BeautifulSoup that extracts specific data from a given website.
      For example, this scraper will extract all the URLs (href attributes) from 'a' tags on the webpage.
      >>> extract_web_data("http://example.com")
      ['http://example.com/page1', 'http://example.com/page2', 'http://example.com/page3']
      """
      import requests
      from bs4 import BeautifulSoup
      
      # Get the web page
      webpage = requests.get(website_url)
      
      # Parse the web page
      soup = BeautifulSoup(webpage.content, 'html.parser')
      
      # Find all 'a' tags
      links = soup.find_all('a')
      
      # Extract the URLs in the 'href' attribute
      extracted_urls = [link.get('href') for link in links]
      
      return extracted_urls
output:     # Filter out None values and return the list of URLs
      return [url for url in extracted_urls if url is not None]