'<' not supported between instances of 'method' and 'method' Django 2.0

Question

I implemented a validation with two methods

def clean(self, *args, **kwargs):
        #valortotal = Venda.objects.filter(id=self.id).aggregate(valortotal=Sum(F('item__produto__valor') * F('item_qtde'), output_field=FloatField()))
        #valor_nota = self.valor_nota
        #if Decimal(valortotal['valortotal']) < valor_nota():
        if self.valortotal < self.valor_nota:
         raise forms.ValidationError("O  valor do Tipo de Pagamento (dinheiro + cartão) não pode ser maior que o valor total da nota.")
        #raise forms.ValidationError(Decimal(valortotal['valortotal']))

and Django returned the following error

Below the methods that return values

def valortotal(self):
        soma = Venda.objects.filter(id=self.id).aggregate(valortotal=Sum(F('item__produto__valor') * F('item__qtde'), output_field=FloatField()))
        return soma['valortotal']

def valor_nota(self, force_insert=False, force_update=False):
        valor_nota = self.valor_dinheiro + self.valor_cartao 
        return valor_nota

The Item Class

class Item(models.Model):
    produto = models.ForeignKey(Produto, on_delete=models.CASCADE, default=None)
    qtde = models.PositiveIntegerField(null=True, blank=False)
    venda = models.ForeignKey(Venda, on_delete=models.CASCADE, default=None)

Answer 1

The message says that on the line where you make the comparison:

if self.valortotal < self.valor_nota:

You are comparing two instances of methods, so the message "< is not supported between instances of methods" ('<' not supported between instances of 'method' and 'method')

To check this, comment the if and print the type of objects involved in the if, with the command:

print('self.valortotal => ', type(self.valortotal))
print('self.valor => ', type(self.valor))

If they are really methods that return values, then change your if to:

if self.valortotal() < self.valor_nota():