Change BooleanField default value to true flask code example

Example: default value for checkbox flask wtf

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In Python file
====================  
uart0_en = BooleanField('Enable UART0', validators=[DataRequired(message='Mandatory')], render_kw={'checked': False})

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In html file
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          <div class="form-group row">
              <div class="col-xs-1">
                    <br>{{ form.uart0_baud.label }}
                    <br>{{ form.uart0_baud }}
              </div>
          </div>