Flask-wtf dynamic select field with an empty option

Question

I want to populate a select field based a query search.

But I also want an empty option.

This is my current code

 form.state.choices=[(s.id, s.name) for s in State.query.all()]

the result is

  <select>
  <option value="CA">California</option>
  <option value="FL">Florida</option>
  </select>

the desired result is

<select>
<option value=""></option>
<option value="CA">California</option>
<option value="FL">Florida</option>
</select>

It would be cool if is also not valid if the select option is empty.

Brewing

Answer 1

You may want to add the empty value like this:

choices = [("", "---")]
form.state.choices=[choices.append((s.id, s.name)) for s in State.query.all()]

Then you can check whether the value is empty string to validate the field.

Obstruent

is there a way to specify a different font for the first tuple? Specifically, the color so that it might be 'greyed out'? – Stiles

It's not working in Python 3.7.3. But work when I use @fab answer. – Resuscitate

[mylist.append(x) for x in some_sequence] will return a list of Nones. – Amaris

I don't know why this is the accepted answer; it's just plain wrong. As @Amaris says, this results in a list of None. Answer from @fab below should be accepted. – Sulphathiazole

Answer 2

You cound add the empty value also in the same line:

form.state.choices=[("", "---")]+[(s.id, s.name) for s in State.query.all()]

Precontract