input: 
  def add_matrix(matrix1, matrix2):
      if len(matrix1) != len(matrix2):
          return 'Matrices not compatible'
      if len(matrix1[0]) != len(matrix2[0]):
          return 'Matrices not compatible'
      
      result = [[matrix1[i][j] + matrix2[i][j] for j in range(len(matrix1[0]))] for i in range(len(matrix1))]
      
      return result
  
  # Examples:
  # add_matrix([[1, 2], [3, 4]], [[2, 3], [4, 5]]) == [[3, 5], [7, 9]]
  # add_matrix([[1, 2]], [[2, 3]]) == [[3, 5]]
  # add_matrix([[1, 2], [3, 4]], [[2, 3]]) == 'Matrices not compatible'
  # add_matrix([[1, 2]], [[2, 3, 4]]) == 'Matrices not compatible'
  
output:     if len(matrix1) != len(matrix2):
          return 'Matrices not compatible'
      if len(matrix1[0]) != len(matrix2[0]):
          return 'Matrices not compatible'
      
      result = [[matrix1[i][j] + matrix2[i][j] for j in range(len(matrix1[0]))] for i in range(len(matrix1))]
      
      return result