input: Write a function to add two matrices. The function should take two matrices as input and return the resulting matrix after addition. If the matrices are not compatible for addition, the function should return 'Matrices not compatible'.
  assert add_matrix([[1, 2], [3, 4]], [[5, 6], [7, 8]])==[[6, 8], [10, 12]]
  assert add_matrix([[1, 2], [3, 4]], [[1], [2]])=='Matrices not compatible'
  assert add_matrix([[1, 2]], [[3, 4]])=='Matrices not compatible'
  assert add_matrix([], [])=='Matrices not compatible'
  assert add_matrix([[1]], [[2]])==[[3]]
output: def add_matrix(matrix1, matrix2):
      if len(matrix1) != len(matrix2) or any(len(row1) != len(row2) for row1, row2 in zip(matrix1, matrix2)):
          return 'Matrices not compatible'
      return [[matrix1[i][j] + matrix2[i][j] for j in range(len(matrix1[0]))] for i in range(len(matrix1))]