default value for checkbox flask wtf
===================
In Python file
====================
uart0_en = BooleanField('Enable UART0', validators=[DataRequired(message='Mandatory')], render_kw={'checked': False})
=============
In html file
=============
<div class="form-group row">
<div class="col-xs-1">
<br>{{ form.uart0_baud.label }}
<br>{{ form.uart0_baud }}
</div>
</div>