input: Write a function to create a class in Python which has two instance variables, title and artist, and three methods, str(), eq(), and length(). The str() method should return the title and artist, the eq() method should check if two Song objects have the same 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("Stairway to Heaven", "Led Zeppelin")
  assert Song("Bohemian Rhapsody", "Queen").length()==15
  assert Song("", "Unknown Artist").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)