input: Write a function to add two matrices. If the matrices are not compatible (i.e., they do not have the same dimensions), return the message 'Matrices not compatible'. Otherwise, return the resulting matrix after addition.
  
  def add_matrix(matrix1, matrix2):
      if len(matrix1) != len(matrix2) or 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
  
  assert add_matrix([[1, 2], [3, 4]], [[5, 6], [7, 8]])==[[6, 8], [10, 12]]
  assert add_matrix([[1, 2]], [[3, 4]])==[[4, 6]]
  assert add_matrix([[1], [2]], [[3], [4]])==[[4], [6]]
  assert add_matrix([[1, 2, 3], [4, 5, 6]], [[7, 8, 9], [10, 11, 12]])==[[8, 10, 12], [14, 16, 18]]
  assert add_matrix([[1, 2], [3, 4]], [[1, 2, 3], [4, 5, 6]])=='Matrices not compatible'
output: def add_matrix(matrix1, matrix2):
      if len(matrix1) != len(matrix2) or 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