input: 
  def add_matrix(matrix1, matrix2):
      """ Given two matrices, return the sum of the two matrices. If the matrices 
          are not equally sized (same number of rows and columns), return 
          'Matrices not compatible'.
      >>> add_matrix([[1, 2], [3, 4]], [[1, 1], [1, 1]])
      [[2, 3], [4, 5]]
      >>> add_matrix([[1, 2], [3, 4]], [[1, 1]])
      'Matrices not compatible'
      """
      if len(matrix1) != len(matrix2):
          return 'Matrices not compatible'
      if len(matrix1[0]) != len(matrix2[0]):
          return 'Matrices not compatible'
      
      result = [[sum(row) for row in zip(*size)] for size in zip(matrix1, matrix2)]
      
      return result
  
output:     result = [[matrix1[i][j] + matrix2[i][j] for j in range(len(matrix1[0]))] for i in range(len(matrix1))]
      return result