order - Django TypeError unsupported operand type(s) for +: 'dict' and 'int' -

i created through model can add order field m2m field having problems auto incrementing order field via def number() below. when add object, typeerror unsupported operand type(s) +: 'dict' , 'int' , i'm not sure why. ideas?

models.py:

class playlist(models.model):     user = models.foreignkey(settings.auth_user_model, default=1)     name = models.charfield(max_length=50)     tracks = models.manytomanyfield(track, through='playlisttrack')      def __str__(self):         return self.name  class playlisttrack(models.model):      def number():         last_order = playlisttrack.objects.all().aggregate(max('order'))         if last_order == none:             return 1         else:             return last_order + 1      track = models.foreignkey(track)     playlist = models.foreignkey(playlist)     order = models.positiveintegerfield(default=number)      class meta:         ordering = ['order'] 

as mentioned in docs, aggregate() returns dict object. hence, variable last_order dict , trying add number dict.

you should value dict , add.

return last_order['order__max'] + 1