old_contents: from django import template
  from django.template.defaultfilters import stringfilter
  
  register = template.Library()
  
  @register.filter(is_safe=True)
  @stringfilter
  def append_form_control(value):
      return value.replace('input', 'input class="form-control"')
  
new_contents: from django import template
  from django.template.defaultfilters import stringfilter
  
  register = template.Library()
  
  
  @register.filter(is_safe=True)
  @stringfilter
  def append_form_control(value):
      return value.replace('input', 'input class="form-control"')
  
subject: Make lint happy