input: Write a function to create a class in Python that matches the given criteria. The class should be named Song and should have two instance variables, title and artist. It should also have three methods: str(), eq(), and length(). The str() method should return a formatted string containing the title and artist. The eq() method should compare the current instance with another instance to check if both title and artist are the same. The length() method should return the length of the title.
  
  class Song:
      def __init__(self, title, artist):
          self.title = title
          self.artist = artist
    
      def __str__(self):
          return f'Title: {self.title}\nArtist: {self.artist}'
      
      def __eq__(self, other):
          return self.artist == other.artist and self.title == other.title
  
      def length(self):
          return len(self.title)
  
  assert str(Song("Shape of You", "Ed Sheeran"))=="Title: Shape of You\nArtist: Ed Sheeran"
  assert Song("Shape of You", "Ed Sheeran")==Song("Shape of You", "Ed Sheeran")
  assert Song("Shape of You", "Ed Sheeran")!=Song("Havana", "Camila Cabello")
  assert Song("Havana", "Camila Cabello").length()==6
  assert Song("", "Unknown").length()==0
output: class Song:
      def __init__(self, title, artist):
          self.title = title
          self.artist = artist
    
      def __str__(self):
          return f'Title: {self.title}\nArtist: {self.artist}'
      
      def __eq__(self, other):
          return self.artist == other.artist and self.title == other.title
  
      def length(self):
          return len(self.title)