how to use choices in django models code example

Example 1: field.choices django

Will create a select box for this in the model form. Use can select from the
options.The first element in each tuple is the actual value to be set on the model, 
and the second element is the human-readable name. For example:
YEAR_IN_SCHOOL_CHOICES = [
        (FRESHMAN, 'Freshman'),
        (SOPHOMORE, 'Sophomore'),
        (JUNIOR, 'Junior'),
        (SENIOR, 'Senior'),
        (GRADUATE, 'Graduate'),
    ]
    year_in_school = models.CharField(
        max_length=2,
        choices=YEAR_IN_SCHOOL_CHOICES,
        default=FRESHMAN,
    )

Example 2: django models choices example

from django.db import models

class Author(models.Model):
   first_name = models.CharField(max_length=64)
   last_name = models.CharField(max_length=64)

   def __str__(self):
       return '{} {}'.format(self.first_name, self.last_name)


class Book(models.Model):
   author = models.ForeignKey('books.Author', related_name='books', on_delete=models.CASCADE)
   title = models.CharField(max_length=128)
   status = models.CharField(
       max_length=32,
       choices=[],  # some list of choices
   )

   def __str__(self):
       return '{}: {}'.format(self.author, self.title)