Python Flask WTForm SelectField With Enum Values 'Not A Valid Choice' Upon Validation

My Python Flask app is using WTForms with built in python Enum support. I'm attempting to submit a form (POST) where a SelectField is populated by all values of a Enum. When I hit

Solution 1:

Is there a way to coerce WTForms

The argument you're looking for is actually called coerce, and it accepts a callable that converts the string representation of the field to the choice's value.

1. The choice value should be an Enum instance
2. The field value should be str(Enum.value)
3. The field text should be Enum.name

To accomplish this, I've extended Enum with some WTForms helpers:

class FormEnum(Enum):
    @classmethod
    def choices(cls):
        return [(choice, choice.name) for choice in cls]

    @classmethod
    def coerce(cls, item):
        return cls(int(item)) if not isinstance(item, cls) else item

    def __str__(self):
        return str(self.value)

You can then edit a FormEnum derived value using a SelectField:

role = SelectField(
        "Role",
        choices = UserRole.choices(),
        coerce = UserRole.coerce)