DateField validation is broken

[crawlchange]

I have a form that has a DateField value. I do this:

print(form.expires_at, file=sys.stderr)
print(type(form.expires_at.data), file=sys.stderr)
print(form.expires_at.data, file=sys.stderr)

The output is:

<input id="expires_at" name="expires_at" required type="date" value="">
<class 'datetime.date'>
2023-04-18

Then, in the next line:

form.validate_on_submit()

"Not a valid date value."

What IS a valid date value? How is a python datetime.date not a valid date value?

[azmeuk]

How is your form initialized?

Please provide a minimal reproducible example ideally something that one can just copy/paste in a python terminal and that demonstrates your issue, like:

>>> import wtforms
>>> class F(wtforms.Form):
...     foo = wtforms.DateField()
>>> f = F(...)
>>> f.validate()
...