code: def _add_ttl_ns(self, line):
          
          lg = logging.getLogger("%s.%s" % (self.ln, inspect.stack()[0][3]))
          lg.setLevel(self.log_level)
  
          lg.debug("line:\n%s", line)
          line = str(line).strip()
          # if the line is not a prefix line exit
          if line is None or line == 'none' or line == '' \
                  or not line.lower().startswith('@prefix'):
              return
          # parse the turtle line
          line = line.replace("@prefix","",1).strip()
          if line.endswith("."):
              line = line[:-1]
          prefix = line[:line.find(":")].strip()
          uri = self.clean_iri(line[line.find(":")+1:].strip())
          # add the namespace to the class
          lg.debug("\nprefix: %s  uri: %s", prefix, uri)
          self.bind(prefix, uri, override=False, calc=False)
docs: takes one prefix line from the turtle file and binds the namespace
          to the class
  
          Args:
              line: the turtle prefix line string