Django migrate error : TypeError expected string or bytes-like object
<p>I'm trying to learn django and error occur in changing models. I tried a lot like default=datetime.datetime.now but I dont know how to fix it.</p>

<p>these are my models</p>

<p>from django.db import models
import datetime</p>

<pre><code>class Candidate(models.Model):
    name = models.CharField(max_length=10)
    introduction = models.TextField()
    area = models.CharField(max_length=15)
    party_number=models.IntegerField(default=0)
    def __str__(self) :
        return self.name

class Poll(models.Model) :
    start_date = models.DateTimeField()
    end_date = models.DateTimeField()
    area = models.CharField(max_length=15)

class Choice(models.Model) :
    poll = models.ForeignKey(Poll)
    candidate = models.ForeignKey(Candidate)
    votes = models.IntegerField(default=0)
</code></pre>

<p>when I type commmand : <code>python manage.py migrate</code>, this error occured</p>

<pre><code>Operations to perform:
  Apply all migrations: admin, ang, auth, contenttypes, sessions
Running migrations:
  Applying ang.0003_poll_end_date...Traceback (most recent call last):
  File "manage.py", line 22, in &lt;module&gt;
    execute_from_command_line(sys.argv)
  File "C:\Python\Python35-32\lib\site-packages\django\core\management\__init__.py", line 367, in execute_from_command_line
    utility.execute()
  File "C:\Python\Python35-32\lib\site-packages\django\core\management\__init__.py", line 359, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "C:\Python\Python35-32\lib\site-packages\django\core\management\base.py", line 294, in run_from_argv
    self.execute(*args, **cmd_options)
  File "C:\Python\Python35-32\lib\site-packages\django\core\management\base.py", line 345, in execute
    output = self.handle(*args, **options)
  File "C:\Python\Python35-32\lib\site-packages\django\core\management\commands\migrate.py", line 204, in handle
    fake_initial=fake_initial,
  File "C:\Python\Python35-32\lib\site-packages\django\db\migrations\executor.py", line 115, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "C:\Python\Python35-32\lib\site-packages\django\db\migrations\executor.py", line 145, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "C:\Python\Python35-32\lib\site-packages\django\db\migrations\executor.py", line 244, in apply_migration
    state = migration.apply(state, schema_editor)
  File "C:\Python\Python35-32\lib\site-packages\django\db\migrations\migration.py", line 129, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "C:\Python\Python35-32\lib\site-packages\django\db\migrations\operations\fields.py", line 84, in database_forwards
    field,
  File "C:\Python\Python35-32\lib\site-packages\django\db\backends\sqlite3\schema.py", line 231, in add_field
    self._remake_table(model, create_fields=[field])
  File "C:\Python\Python35-32\lib\site-packages\django\db\backends\sqlite3\schema.py", line 113, in _remake_table
    self.effective_default(field)
  File "C:\Python\Python35-32\lib\site-packages\django\db\backends\base\schema.py", line 221, in effective_default
    default = field.get_db_prep_save(default, self.connection)
  File "C:\Python\Python35-32\lib\site-packages\django\db\models\fields\__init__.py", line 755, in get_db_prep_save
    prepared=False)
  File "C:\Python\Python35-32\lib\site-packages\django\db\models\fields\__init__.py", line 1438, in get_db_prep_value
    value = self.get_prep_value(value)
  File "C:\Python\Python35-32\lib\site-packages\django\db\models\fields\__init__.py", line 1417, in get_prep_value
    value = super(DateTimeField, self).get_prep_value(value)
  File "C:\Python\Python35-32\lib\site-packages\django\db\models\fields\__init__.py", line 1275, in get_prep_value
    return self.to_python(value)
  File "C:\Python\Python35-32\lib\site-packages\django\db\models\fields\__init__.py", line 1378, in to_python
    parsed = parse_datetime(value)
  File "C:\Python\Python35-32\lib\site-packages\django\utils\dateparse.py", line 93, in parse_datetime
    match = datetime_re.match(value)
TypeError: expected string or bytes-like object
</code></pre>

<p>Please help me!!</p>