def _find(self, texto, patron):
        """Returns the index of the firste element of pattern 'patron' in the list 'texto'.                                                                      
        I.e., if texto=[1,2,3,4,5,6] and patron=[2,3] then _find should return 1."""
        base   = 0
        indice = 0
        try:
            while texto != []:
                indice  = texto.index(patron[0])
                if indice != -1 and texto[indice:indice+len(patron)] != patron:
                    #print "O patron", patron, "non esta na posicion", indice, "ca base", base, "do texto", texto                                                
                    base  += indice + 1
                    texto  = texto[indice + 1:]
                else:
                    break
        except ValueError, IndexError:
            indice = -1
            base   = 0
        return indice + base