It seemed that render_kw in render_form is not working on the "class" property.

[realJustinLee]

https://github.com/greyli/bootstrap-flask/blob/9ca1e7f0a2d3233d781f23da23ad919901a09183/flask_bootstrap/templates/bootstrap/form.html#L235

My code here:

class RegistrationForm(FlaskForm):
    submit = SubmitField('Register', render_kw={'class': 'btn-primary'})

{% from 'bootstrap/form.html' import render_form %}

{{ render_form(form) }}

The return is quite confusing:

<input class="btn btn-secondary" id="submit" name="submit" type="submit" value="Register">

And it seemed that render_form is not passing the render_kw of the SubmitField to the rendered html. This made me confused.

[greyli]

Since we need to add Bootstrap classes when calling this macro in the template, the old class defined with render_kw will be overwritten (it's WTForms's render behavior). You can config button style with button_map:

{{ render_form(form, button_map={'submit': 'primary'}) }}

It maps the field name to the Bootstrap button style, the value can be something like success, info, warning or outline-primary, outline-success, etc.

[realJustinLee]

@greyli Is it possible to append the render_kw after the Bootstrap classes? I consider this would be a much better way to achieve a more developer friendly solution.

[greyli]

Just fix this in 708111a. Besides, this PR will bring a config called BOOTSTRAP_BTN_STYLE, you can use it to set a global button default style.