text: from django.conf import settings
  from django.core.exceptions import ValidationError
  
  
  def validate_only_one_instance(obj):
      """
      Allow only one instance
      """
      model = obj.__class__
      if (model.objects.count() > 0 and obj.id != model.objects.get().id):
          raise ValidationError("We're sorry but a %s already exists, only one is allowed." % model.__name__)
  
  
  def replace_tags(string=None, tags=dict()):
      """
      Replace tags from a given string
      """
      if string is None:
          raise TypeError("string type needed")
      else:
          for key, value in tags.items():
              string = string.replace(key, value)
      return string
  
  
  def has_recaptcha():
      """
      Check if the WagtailCaptcha settings are properly set
      """
      wagtailcaptcha_public_key = getattr(settings, 'RECAPTCHA_PUBLIC_KEY', None)
      wagtailcaptcha_private_key = getattr(settings, 'RECAPTCHA_PRIVATE_KEY', None)
  
      return wagtailcaptcha_public_key and wagtailcaptcha_private_key
  