docs: def update(instance, full_clean=True, post_save=False, **kwargs):
      "Atomically update instance, setting field/value pairs from kwargs"
  
      # apply the updated args to the instance to mimic the change
      # note that these might slightly differ from the true database values
      # as the DB could have been updated by another thread. callers should
      # retrieve a new copy of the object if up-to-date values are required
      for k, v in kwargs.iteritems():
          if isinstance(v, ExpressionNode):
              v = resolve_expression_node(instance, v)
          setattr(instance, k, v)
  
      # clean instance before update
      if full_clean:
          instance.full_clean()
  
      # fields that use auto_now=True should be updated corrected, too!
      for field in instance._meta.fields:
          if hasattr(field, 'auto_now') and field.auto_now and field.name not in kwargs:
              kwargs[field.name] = field.pre_save(instance, False)
  
      rows_affected = instance.__class__._default_manager.filter(
          pk=instance.pk).update(**kwargs)
  
      if post_save:
          signals.post_save.send(sender=instance.__class__, instance=instance)
  
      return rows_affected