input: from typing import List
  
  def extract_top_ten_trending_videos() -> List[str]:
      """ Implement a web scraper to extract the top ten trending YouTube videos and return their titles as a list of strings.
      >>> extract_top_ten_trending_videos()
      ['Video 1 Title', 'Video 2 Title', 'Video 3 Title', 'Video 4 Title', 'Video 5 Title', 'Video 6 Title', 'Video 7 Title', 'Video 8 Title', 'Video 9 Title', 'Video 10 Title']
      """
output:     import requests
      from bs4 import BeautifulSoup
  
      url = "https://www.youtube.com/feed/trending"
      response = requests.get(url)
      soup = BeautifulSoup(response.text, 'html.parser')
  
      video_titles = []
      for video in soup.find_all('a', {'class': 'yt-simple-endpoint style-scope ytd-video-renderer'}):
          title = video.get('title')
          if title:
              video_titles.append(title)
          if len(video_titles) == 10:
              break
  
      return video_titles