How can I add a value to a WTForms Submit field without changing its display label?

Question

When I set a value for the field it changes the display label of the field. I'm using FlaskWTForms and the field is defined as:

class EditMultilpeChoiceQuestion(FlaskForm):

    submit_update = SubmitField(name="submit_update", label="Update question")

In the Jinja template the code to display the field is:

{{ form.submit_update(class="btn btn-primary btn-sm" value=question['database_id']) }}

Is this example the value of question['database_id'] is 10 and the field display as:

button display with value parameter added

If I don't have the value=question['database_id'] the field displays as I want:

button display with no value parameter

any suggestions much appreciated.

Answer 1

The widget used to render a submit field is a SubmitInput, Github source, as shown below:

class SubmitInput(Input):
    """
    Renders a submit button.

    The field's label is used as the text of the submit button instead of the
    data on the field.
    """

    input_type = "submit"

    def __call__(self, field, **kwargs):
        kwargs.setdefault("value", field.label.text)
        return super().__call__(field, **kwargs)

Note the comment:

The field's label is used as the text of the submit button instead of the data on the field.

See simple test code below:

from wtforms.fields import SubmitField
from wtforms.form import Form


class F(Form):
    a = SubmitField(label="Update question")


def test_submit_field():
    # Pass no args
    _html = F().a()
    print(_html)
    assert _html == """<input id="a" name="a" type="submit" value="Update question">"""

    # assigning the value clears the label
    _html = F().a(value=10)
    print(_html)
    assert _html == """<input id="a" name="a" type="submit" value="10">"""

    # assign label and value
    _html = F().a(label="Hello World", value=10)
    print(_html)
    assert _html == """<input id="a" label="Hello World" name="a" type="submit" value="10">"""


if __name__ == "__main__":
    test_submit_field()