How to filter a query_set for unique Django values

I'm trying to get unique value results from a query_set in django. What I want is for you to return me as many unique classifications There is.

Example. In a Table I have different articles that are classified by type

ID     |    NOMBRE    |    CLASIFICACION
1           Escoba         Limpieza
2           Trapeador      Limpieza
3           Tornillo       Herramienta

I want you to return me 2 classifications Cleaning and Tool. he currently returns me the 3 classifications Cleaning, Cleaning and tool.

my view:

class ItemListView(ListView):
    model= Items

    def get_context_data(self,**kwargs):
        context = super(ItemListView, self).get_context_data(**kwargs)
        context['clasificacion'] = Items.objects.order_by('nombre').distinct('clasificacion')
        return context

My Models

from django.db import models

# Create your models here.
class Items(models.Model):
    nombre = models.CharField(max_length=250)
    descripcion = models.CharField(max_length=250)
    codigo_proveedor = models.CharField(max_length=250)
    clasificacion = models.CharField(max_length=250)
    c_minima = models.IntegerField()
    c_actual = models.IntegerField()
    proveedor = models.ForeignKey('Proveedores', 
                on_delete=models.CASCADE)
    active = models.BooleanField()

        def __str__(self):
            return self.nombre + '   -----   ' + 
                   self.clasificacion + '   -----    ' + 
                   str(self.c_actual)


class Proveedores(models.Model):
    nombre = models.CharField(max_length=250)
    telefono = models.CharField(max_length=250)
    direccion1 = models.CharField(max_length=250)
    direccion2 = models.CharField(max_length=250, null=True)
    active =  models.BooleanField()

    def __str__(self):
        return self.nombre

I would appreciate your help