input: Write a function to create a web scraper that extracts specific data from a given website using the BeautifulSoup Python package. The function should find HTML elements on the webpage using tags and attributes, convert the data into the desired format, and store it.
  
  def web_scraper(url):
      import requests
      from bs4 import BeautifulSoup
      
      # Get the web page
      webpage = requests.get(url)
      
      # Parse the web page
      soup = BeautifulSoup(webpage.content, 'html.parser')
      
      # Find all 'a' tags and extract the URLs in the 'href' attribute
      links = [link.get('href') for link in soup.find_all('a')]
      
      return links
  
  assert web_scraper("http://example.com")==['/sample_link1', '/sample_link2']
  assert web_scraper("http://another_example.com")==['/link1', '/link2', '/link3']
  assert web_scraper("")==[]
output: def web_scraper(url):
      import requests
      from bs4 import BeautifulSoup
      
      if not url:
          return []
      
      webpage = requests.get(url)
      soup = BeautifulSoup(webpage.content, 'html.parser')
      links = [link.get('href') for link in soup.find_all('a')]
      
      return links