gistfile1.py

import wtforms


class DummyPostData(dict):
    def getlist(self, key):
        v = self[key]
        if not isinstance(v, (list, tuple)):
            v = [v]
        return v


class MyForm(wtforms.Form):
    datetime_field = wtforms.DateTimeField(
        validators=[wtforms.validators.Required()]
    )


post_data = DummyPostData({'datetime_field': '2013-09-24 00:00'})
form = MyForm(post_data)
form.validate()

# this fails validation because the format doesn't match the field's format

# however, when the Required() validator is on the field, like it is above,
# the error message is:

In [2]: form.errors
Out[2]: {'datetime_field': [u'This field is required.']}

# instead of 'Not a valid datetime value', which is what it should be