code: def close_fd(self, fd):
          
          try:
              try:
                  fd.close()
              except AttributeError:
                  os.close(fd)
          except OSError:
              pass
docs: Utility method to close an ``fd``.
  
          If ``fd`` is a file-like object, we close it directly; otherwise
          we use `os.close`.
  
          This method is provided for use by `IOLoop` subclasses (in
          implementations of ``IOLoop.close(all_fds=True)`` and should
          not generally be used by application code.
  
          .. versionadded:: 4.0