from django.db import models
class Author(models.Model):
	first_name = models.CharField(max_length=30)
	last_name = models.CharField(max_length=40)
	email = models.EmailField()
	
class Book(models.Model):
	title = models.CharField(max_length=100)
	date = models.CharField(max_length=20)
	author = models.ForeignKey(Author)

You are trying to add a non-nullable field 'author' to book without a default; we can't do that (the database needs something to populate existing rows).
Please select a fix:
 1) Provide a one-off default now (will be set on all existing rows)
 2) Quit, and let me add a default in models.py
Select an option: 1
Please enter the default value now, as valid Python
The datetime and django.utils.timezone modules are available, so you can do e.g. timezone.now()