database sequence

>>> import contextlib
>>> from django.db import models
>>> 
>>> class Sequence(models.Model):
...     pass
>>> 
>>> @contextlib.contextmanager
>>> def unique_threadsafe_id():
...     try: 
...         a, created = Sequence.objects.create()
...         yield a.pk
...     finally:
...         a.delete()
>>> 
>>> 
>>> with unique_threadsafe_id() as id:
...     print id
1 
>>> with unique_threadsafe_id() as id:
...     print id
2 
>>> 
>>> 
>>> print Sequence.objects.get()
Exception Sequence.DoesNotExist
    ...