Setting a non-existent attribute fails silently

[medwig]

Attempting to set an attribute that doesn't exist has no effect. This makes typos when setting attributes very dangerous. I think this should raise an AttributeError.

from pynamodb.models import Model
from pynamodb.attributes import UnicodeAttribute

class User(Model):
    class Meta:
        table_name = 'test-user-table'
        region = 'us-west-2'
        write_capacity_units = 1
        read_capacity_units = 1
    user_id = UnicodeAttribute(hash_key=True)
    name = UnicodeAttribute()

if not User.exists():
        User.create_table(wait=True)

user_item = User('user-1', name='John Doe')
user_item.email = 'foo@bar.com'
print(user_item.attribute_values)

User.delete_table()

{'name': 'New Name', 'user_id': 'user-1'}

[jpinner-lyft]

@medwig your statement that setting the email attribute had no affect isn't completely accurate. The attribute is set on the Model in the object's __dict__ the same as any other python object:

>>> user_item.__dict__
{'attribute_values': {'user_id': 'user-1', 'name': 'John Doe'}, 'email': 'foo@bar.com'}

Now you are correct that email will not be stored in Dynamo since it is not defined as an Attribute.

[jpinner-lyft]

@jmphilli @garrettheel we could consider removing the __dict__ attribute on the Model class which would allow users to define a __slots__ field on their subclasses. Thoughts?

[garrettheel]

@jpinner-lyft this would mean people couldn't add attributes dynamically after class instantiation? If so, that seems reasonable but we should check to make sure it's not going to break anyone.

The advantage you're looking for is lower memory consumption?

[jpinner-lyft]

@garrettheel If someone wanted to prevent adding attributes on their Model sub-classes, they would define a __slots__ attribute on their subclass. This doesn't work because the Model class has a __dict__ attribute so any new attributes will just get stored on Model.

One solution would be to remove __dict__ from Model. Users who wanted to dynamically add attributes on their subclasses could still do so since the subclass would have a __dict__ attribute. Users who didn't could use then use the __slots__ mechanism on their subclass since new attributes could not be stored on Model.