input: Write a python function to predict a genre for a new song given its artist, title, and lyrics.
  assert predict_genre('artist1', 'title1', 'sample lyrics for song 1') in ['pop', 'rock', 'jazz']
  assert predict_genre('artist2', 'title2', 'sample lyrics for song 2') in ['pop', 'rock', 'jazz']
  assert predict_genre('artist3', 'title3', 'sample lyrics for song 3') in ['pop', 'rock', 'jazz']
output: def predict_genre(artist, title, lyrics):
      # Placeholder function for predicting genre
      # In a real-world scenario, you would use a trained machine learning model
      # For this example, we'll use a simple heuristic
  
      if 'love' in lyrics or 'heart' in lyrics:
          return 'pop'
      elif 'guitar' in lyrics or 'band' in lyrics:
          return 'rock'
      elif 'saxophone' in lyrics or 'jazz' in lyrics:
          return 'jazz'
      else:
          # Default to pop for simplicity
          return 'pop'