input: Write a function to add two matrices. If the matrices are not compatible (different number of rows or columns), return 'Matrices not compatible'. Otherwise, return the resulting matrix.
  
  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]], [[5,6]])=='Matrices not compatible'
  assert add_matrix([[1,2],[3,4]], [[5,6],[7,8],[9,10]])=='Matrices not compatible'
  assert add_matrix([[1,2],[3,4]], [[5,6],[7]])=='Matrices not compatible'
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))]