input: 
  from typing import List
  
  def add_matrix(matrix1: List[List[int]], matrix2: List[List[int]]) -> List[List[int]]:
      """ Adds two matrices together. If the matrices are not the same size, returns
      'Matrices not compatible'.
      >>> add_matrix([[1, 2], [3, 4]], [[5, 6], [7, 8]])
      [[6, 8], [10, 12]]
      >>> add_matrix([[1, 2], [3, 4]], [[5, 6]])
      'Matrices not compatible'
      """
      if len(matrix1) != len(matrix2) or all(len(m1) == len(m2) for m1, m2 in zip(matrix1, matrix2)):
          return 'Matrices not compatible'
      
      return [[m1 + m2 for m1, m2 in zip(row1, row2)] for row1, row2 in zip(matrix1, matrix2)]
  
output:     
      if len(matrix1) != len(matrix2) or any(len(m1) != len(m2) for m1, m2 in zip(matrix1, matrix2)):
          return 'Matrices not compatible'
      
      return [[m1 + m2 for m1, m2 in zip(row1, row2)] for row1, row2 in zip(matrix1, matrix2)]
  