from django.db import models
from django.utils.translation import ugettext_lazy as _

class TaxGroup(models.Model):

    name = models.CharField(_("group name"), max_length=100)
    rate = models.DecimalField(_("rate"), max_digits=4, decimal_places=2,
                               help_text=_("Percentile rate of the tax."))
    rate_name = models.CharField(_("name of the rate"), max_length=30,
                                 help_text=_("Name of the rate which will be"
                                             " displayed to the user."))
    def __unicode__(self):
        return self.name


class TaxedProductMixin(models.Model):

    tax_group = models.ForeignKey(TaxGroup, related_name='products',
                                  null=True)

from django.db import models
from django.utils.translation import ugettext_lazy as _

class TaxGroup(models.Model):

    name = models.CharField(_("group name"), max_length=100)
    rate = models.DecimalField(_("rate"), max_digits=4, decimal_places=2,
                               help_text=_("Percentile rate of the tax."))
    rate_name = models.CharField(_("name of the rate"), max_length=30,
                                 help_text=_("Name of the rate which will be"
                                             " displayed to the user."))
    def __unicode__(self):
        return self.name


class TaxedProductMixin(models.Model):

    tax_group = models.ForeignKey(TaxGroup, related_name='products',
                                  null=True)
    class Meta:
        abstract = True

Fix - TaxedProductMixin is abstract model
Fix - TaxedProductMixin is abstract model

  from django.db import models
  from django.utils.translation import ugettext_lazy as _
  
  class TaxGroup(models.Model):
  
      name = models.CharField(_("group name"), max_length=100)
      rate = models.DecimalField(_("rate"), max_digits=4, decimal_places=2,
                                 help_text=_("Percentile rate of the tax."))
      rate_name = models.CharField(_("name of the rate"), max_length=30,
                                   help_text=_("Name of the rate which will be"
                                               " displayed to the user."))
      def __unicode__(self):
          return self.name
  
  
  class TaxedProductMixin(models.Model):
  
      tax_group = models.ForeignKey(TaxGroup, related_name='products',
                                    null=True)
+     class Meta:
+         abstract = True
  
Fix - TaxedProductMixin is abstract model
## Code Before:
from django.db import models
from django.utils.translation import ugettext_lazy as _

class TaxGroup(models.Model):

    name = models.CharField(_("group name"), max_length=100)
    rate = models.DecimalField(_("rate"), max_digits=4, decimal_places=2,
                               help_text=_("Percentile rate of the tax."))
    rate_name = models.CharField(_("name of the rate"), max_length=30,
                                 help_text=_("Name of the rate which will be"
                                             " displayed to the user."))
    def __unicode__(self):
        return self.name


class TaxedProductMixin(models.Model):

    tax_group = models.ForeignKey(TaxGroup, related_name='products',
                                  null=True)

## Instruction:
Fix - TaxedProductMixin is abstract model
## Code After:
from django.db import models
from django.utils.translation import ugettext_lazy as _

class TaxGroup(models.Model):

    name = models.CharField(_("group name"), max_length=100)
    rate = models.DecimalField(_("rate"), max_digits=4, decimal_places=2,
                               help_text=_("Percentile rate of the tax."))
    rate_name = models.CharField(_("name of the rate"), max_length=30,
                                 help_text=_("Name of the rate which will be"
                                             " displayed to the user."))
    def __unicode__(self):
        return self.name


class TaxedProductMixin(models.Model):

    tax_group = models.ForeignKey(TaxGroup, related_name='products',
                                  null=True)
    class Meta:
        abstract = True
