how to implement not-required DateField using Flask-WTF

Question

I want a DateField which is optional, but I got a "Not a valid date value" error if leave it empty

I add some logs in the source code of wtforms, and found formdata.getlist(self.name) returns [u''] for this DateField

The code of my form:

from wtforms import BooleanField, TextField, TextAreaField, PasswordField, validators, HiddenField, DateField, SelectField from flask_wtf import Form  class EmployeeForm(Form):     id = HiddenField('id')     title = TextField('Title')     start = DateField('Start Date', format='%m/%d/%Y') 

Answer 1

You are looking for the Optional validator.

start = DateField('Start Date', format='%m/%d/%Y', validators=(validators.Optional(),)) 

Answer 2

Quite and old topic, but someone might still run into the same problem, so I'll put my possible answer for that. Adding validators.Optional() does not help here, because the field is marked as error earlier during the processing stage.
You can patch the processor's behaviour like this:

class NullableDateField(DateField):     """Native WTForms DateField throws error for empty dates.     Let's fix this so that we could have DateField nullable."""     def process_formdata(self, valuelist):         if valuelist:             date_str = ' '.join(valuelist).strip()             if date_str == '':                 self.data = None                 return             try:                 self.data = datetime.datetime.strptime(date_str, self.format).date()             except ValueError:                 self.data = None                 raise ValueError(self.gettext('Not a valid date value'))