input: 
  def add_matrix(matrix1, matrix2):
      """ Adds two matrices. Returns 'Matrices not compatible' if the matrices are of different dimensions.
      >>> add_matrix([[1, 2], [3, 4]], [[2, 4], [6, 8]])
      [[3, 6], [9, 12]]
      >>> add_matrix([[1, 2], [3, 4]], [[2, 4]])
      'Matrices not compatible'
      """
      if len(matrix1) != len(matrix2):
          return 'Matrices not compatible'
      if len(matrix1[0]) != len(matrix2[0]):
          return 'Matrices not compatible'
      
      rows = len(matrix1)
      cols = len(matrix1[0])
      result = [list(map(sum, zip(*rows))) for rows in zip(matrix1, matrix2)]
      
      return result
  
output:     
      rows = len(matrix1)
      cols = len(matrix1[0])
      result = [[matrix1[i][j] + matrix2[i][j] for j in range(cols)] for i in range(rows)]
      
      return result
  