python - Error in Django model ValueError -

i getting error on running python manage.py syncdb , python manage.py migrate

the model working fine tried add model object , on running migrate commond displayed error.

so reverted original models.py still showing error.

my project's models.py following:

from django.db import models django.conf import settings   class assignment(models.model):     main_sub     = models.charfield(max_length="60", choices=settings.subjects_list, default ='sub1')     add_sub      = models.charfield(max_length="60", choices=settings.subjects_list, default ='sub1')     deadline     = models.charfield(max_length="60", choices=settings.due_time_list, default ='12 hours')     details      = models.textfield()     timestamp    = models.datetimefield(auto_now_add=true, auto_now=false)     username     = models.charfield(max_length="60")      def __unicode__(self):         return self.username 

and on running syncdb output is:

http://pastebin.com/zfp2mz1z

i have looked questions related error nothing helped.

subjects_list , due_time_list tuples:

#dropdown subjects subjects_list = (         ( 'sub1', 'subject1' ),         ( 'sub2', 'subject2' ),         ( 'sub3','subject3' ),     )  #dropdown due_time due_time_list = (         ( '12 hours', '12 hours' ),         ( '24 hours', '24 hours' ),         ( '2 days','2 days' ),         ( '3 days','3 days' ),         ( '4 days','4 days' ),         ( '5 days','5 days' ),         ( '6 days','6 days' ),         ( '1 week','1 week' ),         ( 'more 1 week','more 1 week' ),     )