input: Write a function to create a Python class Song with two instance variables, title and artist, and three methods, str(), eq(), and length(). The str() method should return a formatted string with the title and artist, the eq() method should compare the equality of two Song objects based on their title and artist, and 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("Bohemian Rhapsody", "Queen")) == 'Title: Bohemian Rhapsody\nArtist: Queen'
  assert Song("Bohemian Rhapsody", "Queen") == Song("Bohemian Rhapsody", "Queen")
  assert Song("Bohemian Rhapsody", "Queen") != Song("Billie Jean", "Michael Jackson")
  assert Song("Abcdef", "Unknown").length() == 6
  assert Song("A", "Single").length() == 1
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)