title: Python Flask WTForms datetime validate another
body: <p>Is it possible to do validation on a datetime field in WTForms comparing it to another datetime?</p>
  
  <p>I have the form</p>
  
  <pre><code>class EventEdit(FlaskForm):
  timeIn = DateTimeField('Time In', validators=[DataRequired()])
  timeOut = DateTimeField('Time Out', validators=[DataRequired()])
  reason = RadioField('Reason', choices=[
      ('Incident','Incident'),
      ('Gym','Gym'),
      ('Meeting','Meeting'),
      ('Other','Other')])
  comment = StringField('Additional Comments')
  submit = SubmitField('Save Changes')
  </code></pre>
  
  <p>I need to make sure when timeOut is entered it is greater than timeIn.</p>
  
  <p>Additionally, I haven't been able to get the timeOut field to be optional yet either.</p>
  
  <p>Thanks in advance.</p>