Peewee calls __init__ on model unexpectedly

We’ve run into some trouble when upgrading to peewee 2.8.0, when we have a custom __init__ defined on our models. This behaviour worked fine when on earlier versions (2.7.3 is the other version I tested).

import peewee as pw

db = pw.SqliteDatabase(':memory:')


class TestTable1(pw.Model):

    a = pw.IntegerField()
    b = pw.IntegerField(default=2)

    class Meta:
        database = db


class TestTable2(pw.Model):

    def __init__(self, a=2):
        pw.Model.__init__(self, a=a)

    a = pw.IntegerField()
    b = pw.IntegerField(default=2)

    class Meta:
        database = db


db.connect()

db.create_tables([TestTable1, TestTable2])

# This works fine
TestTable1.create(a=2)
t1 = TestTable1.select().get()

# This fails
TestTable2.create(a=2)
t2 = TestTable2.select().get()  # Failure with: TypeError: __init__() got an unexpected keyword argument 'b'

In the code above, the failure occurs in the final select, it seems that when the model instance is created, the code in playhouse._speedups._ModelQueryResultWrapper.process_row uses __init__ to create an instance of the row with the full results of the query passed as kwargs (i.e. a=2, b=2). However, the TestTable2.__init__ does not support b as a keyword argument.

It’s not clear from the documentation how well I should expect custom __init__ methods to work. However, I would imagine that this could be fixed by making playhouse._speedups._ModelQueryResultWrapper.process_row explicitly call pw.Model.__init__ on an instance created via __new__.

[coleifer]

You can still put it in __init__() with the caveat that __init__() is going to be called not just when instantiating objects yourself, but also every time a Car instance is read from a database cursor. I think you probably could make a classmethod on your Car object and use that as a factory for complex logic?

[lez]

Try modifying your __init__ to:

def __init__(self, a=2, **kwargs):
    pw.Model.__init__(self, a=a, **kwargs)