input: 
  def visualize_twitter_data(tweets: dict) -> None:
      """
      Visually summarizes the given Twitter data by creating three bar charts: one for the number of tweets per author, one for the number of likes per tweet, and one for the number of retweets per tweet.
      >>> visualize_twitter_data({
      ...     'tweet1': {'author': 'user1', 'likes': 10, 'retweets': 5},
      ...     'tweet2': {'author': 'user2', 'likes': 15, 'retweets': 7},
      ...     'tweet3': {'author': 'user1', 'likes': 20, 'retweets': 3}
      ... })
      # Should generate three charts as described in the function.
      """
      import matplotlib.pyplot as plt
  
      # Initialize dictionaries to accumulate data
      authors_count = {}
      likes_count = {}
      retweets_count = {}
  
      # Process the Twitter data to extract the relevant data fields
      for tweet_id, tweet_info in tweets.items():
          author = tweet_info['author']
          likes = tweet_info['likes']
          retweets = tweet_info['retweets']
          
          # Count tweets per author
          if author in authors_count:
              authors_count[author] += 1
          else:
              authors_count[author] = 1
          
          # Count total likes per tweet
          likes_count[tweet_id] = likes
          
          # Count total retweets per tweet
          retweets_count[tweet_id] = retweets
  
      # Plot the tweet authors
      authors = list(authors_count.keys())
      num_tweets = list(authors_count.values())
      plt.bar(authors, num_tweets)
      plt.xlabel('Tweet Authors')
      plt.ylabel('Number of tweets')
      plt.title('Tweet Author Summary')
      plt.show()
  
      # Plot the number of likes
      tweets_likes = list(likes_count.keys())
      num_likes = list(likes_count.values())
      plt.bar(tweets_likes, num_likes)
      plt.xlabel('Tweets')
      plt.ylabel('Number of Likes')
      plt.title('Number of Likes Summary')
      plt.show()
  
      # Plot the number of retweets
      tweets_retweets = list(retweets_count.keys())
      num_retweets = list(retweets_count.values())
      plt.bar(tweets_retweets, num_retweets)
      plt.xlabel('Tweets')
      plt.ylabel('Number of Retweets')
      plt.title('Number of Retweets Summary')
      plt.show()
  
output:     
      # Plot the tweet authors
      authors = list(authors_count.keys())
      num_tweets = list(authors_count.values())
      plt.bar(authors, num_tweets)
      plt.xlabel('Tweet Authors')
      plt.ylabel('Number of tweets')
      plt.title('Tweet Author Summary')
      plt.show()
  
      # Plot the number of likes
      tweets_likes = list(likes_count.keys())
      num_likes = list(likes_count.values())
      plt.bar(tweets_likes, num_likes)
      plt.xlabel('Tweets')
      plt.ylabel('Number of Likes')
      plt.title('Number of Likes Summary')
      plt.show()
  
      # Plot the number of retweets
      tweets_retweets = list(retweets_count.keys())
      num_retweets = list(retweets_count.values())
      plt.bar(tweets_retweets, num_retweets)
      plt.xlabel('Tweets')
      plt.ylabel('Number of Retweets')
      plt.title('Number of Retweets Summary')
      plt.show()
  