add new editor to "Editors" group.

from django.contrib.auth.models import (
    PermissionsMixin,
    BaseUserManager,
    AbstractBaseUser,
    Permission,
    Group
)
from django.db import models
from django.utils import timezone


class UserManager(BaseUserManager):
    def create_user(self, email, dob, accepted_tos=None, password=None):
        if not accepted_tos:
            raise ValueError("Users must accept the terms of service")

        user = self.model(
            email=self.normalize_email(email),
            dob=dob,
            accepted_tos=True
        )
        user.set_password(password)
        user.save()
        return user

    def create_superuser(self, email, dob, password):
        user = self.create_user(
            email,
            dob,
            accepted_tos=True,
            password=password
        )
        user.is_staff = True
        user.is_superuser = True
        user.save()
        return user

    def create_editor(self, email, dob, password):
        user = self.create_user(
            email,
            dob,
            accepted_tos=True,
            password=password
        )
        try:
            editors = Group.objects.get(name__iexact="Editors")
            user.groups.add(editors)
            user.save()
        except Group.DoesNotExist:
            editors = Group.objects.create(name="Editors")
            editors.permissions.add(Permission.objects.get(codename="can_give_discount"))
            user.groups.add(editors)
            user.save()
        return user

class User(AbstractBaseUser, PermissionsMixin):
    email = models.EmailField(unique=True)
    dob = models.DateField()
    accepted_tos = models.BooleanField()
    is_staff = models.BooleanField(default=False)
    joined_at = models.DateTimeField(default=timezone.now)

    objects = UserManager()

    USERNAME_FIELD = "email"
    REQUIRED_FIELDS = ["dob"]