peewee_first.py

from peewee import *

database = SqliteDatabase(':memory:')

class Model(Model):
    class Meta:
        database = database


class User(Model):
    username = CharField()

User.create_table()

User.create(username="foo")

print User.select().count() # prints 1

user = User.select(User.username).first()
user.username = "bar"
user.save()  # this one generates INSERT instead of UPDATE

print User.select().count() # prints 2