input: Write a program to visualize Twitter data by plotting various summaries of the data fields such as tweet authors, number of likes, and number of retweets.
  assert visualize_twitter_data([])==None
  assert visualize_twitter_data([{'author': 'Alice', 'likes': 10, 'retweets': 5}, {'author': 'Bob', 'likes': 15, 'retweets': 8}])
  assert visualize_twitter_data([{'author': 'Alice', 'likes': 10, 'retweets': 5}, {'author': 'Bob', 'likes': 15, 'retweets': 8}, {'author': 'Charlie', 'likes': 20, 'retweets': 12}])
  assert visualize_twitter_data([{'author': 'Alice', 'likes': 10, 'retweets': 5}, {'author': 'Bob', 'likes': 15, 'retweets': 8}, {'author': 'Charlie', 'likes': 20, 'retweets': 12}, {'author': 'Alice', 'likes': 12, 'retweets': 6}])
output: 
  def visualize_twitter_data(data):
      if not data:
          return None
      
      authors = [tweet['author'] for tweet in data]
      likes = [tweet['likes'] for tweet in data]
      retweets = [tweet['retweets'] for tweet in data]
      
      import matplotlib.pyplot as plt
      
      fig, ax = plt.subplots(3, 1, figsize=(10, 15))
      
      ax[0].bar(authors, likes)
      ax[0].set_title('Number of Likes by Author')
      ax[0].set_xlabel('Author')
      ax[0].set_ylabel('Likes')
      
      ax[1].bar(authors, retweets)
      ax[1].set_title('Number of Retweets by Author')
      ax[1].set_xlabel('Author')
      ax[1].set_ylabel('Retweets')
      
      ax[2].scatter(likes, retweets)
      ax[2].set_title('Likes vs Retweets')
      ax[2].set_xlabel('Likes')
      ax[2].set_ylabel('Retweets')
      
      plt.tight_layout()
      plt.show()
  