Validating SQLAlchemy enum before a save operaiton

Question

Consider the following column definition:

group_name = db.Column(db.Enum('dogs', 'cats', name='device_group'))

Then in my API function I do:

lassie.group_name = userData.group
db.session.add(obj)
db.session.commit()

The problem that even if userData.group is treated as string in Python. Even if its value is "bird", until I actually do the commit operation, I will get no exception.

• Why is SQLAlchemy is treating group_name as a string and not an enum?
• How can I validate that the value I am putting on the object is an enum?
• Should I perhaps use SQLAlchemy validator for that?