code: def add_form_widget_attr(field, attr_name, attr_value, replace=0):
      
      if not replace:
          attr = field.field.widget.attrs.get(attr_name, '')
          attr += force_text(attr_value)
          field.field.widget.attrs[attr_name] = attr
          return field
      else:
          field.field.widget.attrs[attr_name] = attr_value
          return field
docs: Adds widget attributes to a bound form field.
  
      This is helpful if you would like to add a certain class to all your forms
      (i.e. `form-control` to all form fields when you are using Bootstrap)::
  
          {% load libs_tags %}
          {% for field in form.fields %}
              {% add_form_widget_attr field 'class' 'form-control' as field_ %}
              {{ field_ }}
          {% endfor %}
  
      The tag will check if the attr already exists and only append your value.
      If you would like to replace existing attrs, set `replace=1`::
  
          {% add_form_widget_attr field 'class' 'form-control' replace=1 as
            field_ %}