title: Sum numbers of each row of a matrix Python
body: <pre><code>lista = [[1,2,3],[4,5,6],[7,8,9]]
  
  print(lista)
  
  def filas(lista):
  
      res=[]
      for elemento in lista:
          x = sum(lista[elemento])
          res.append(x)
      print(res)
  </code></pre>
  
  <p>I need to sum the numbers of each row, and then print it as a list. It seems the problem I have is that I try to sum the sublists, instead of the numbers of each row.</p>