How can I use a HiddenField to coerce integer data in WTForms?

Question

I have a WTForm class like so:

class MyForm(Form):
    field1 = HiddenField(default=0, validators=NumberRange(min=0, max=20)])

consider this markup as rendered by WTForms

<input type='hidden' name='field1' value='5'></input>

This does not pass the NumberRange validation. This is because HiddenFields widget class coerces the value attribute into a string. How can I get WTForms to produce this markup such that I can perform numeric validation on the subsequent POST?

Answer 1

The recommended trick is to use an IntegerField and change the widget to a HiddenInput

class MyForm(Form):
    field1 = IntegerField(widget=HiddenInput())

you can also subclass

class HiddenInteger(IntegerField):
    widget = HiddenInput()