code: def find_by_fileext(fileext, prs):
      
      def pred(pcls):
          """Predicate"""
          return fileext in pcls.extensions()
  
      pclss = findall_with_pred(pred, prs)
      if not pclss:
          raise UnknownFileTypeError("file extension={}".format(fileext))
  
      return pclss
docs: :param fileext: File extension
      :param prs: A list of :class:`anyconfig.models.processor.Processor` classes
      :return: A list of processor class to processor files with given extension
      :raises: UnknownFileTypeError