Not getting IntegrityError

#!/usr/bin/env python3
# encoding: utf-8

from peewee import *

db = SqliteDatabase("students.db")


class Student(Model):

    # no username -> error
    username = CharField(max_length=255, unique=True)
    points = IntegerField(default=0)

    class Meta:
        database = db


students = [
    {"username": "dmr",
     "points": 4888},
    {"username": "ken",
     "points": 420},
    {"username": "sc3",
     "points": 34},
]


def add_students():
    for student in students:
        try:
            Student.create(username=student["username"],
                       points=student["points"])
        except IntegrityError:
            student_record = Student.get(username=student["username"])
            student_record.points = student["points"]
            student_record.save()


if __name__ == "__main__":
    db.connect()
    db.create_tables([Student], safe=True)
    add_students()