first commit

core/apps/accounts/signals/user.py

@@ -0,0 +1,10 @@
+from django.db.models.signals import post_save
+from django.dispatch import receiver
+from django.contrib.auth import get_user_model
+
+
+@receiver(post_save, sender=get_user_model())
+def user_signal(sender, created, instance, **kwargs):
+    if created and instance.username is None:
+        instance.username = "U%(id)s" % {"id": 1000 + instance.id}
+        instance.save()