code: def setnchannels(self, nchannels):
      if self._nframeswritten:
          raise Error(
              "cannot change parameters after starting to write"
          )
      if nchannels not in (1, 2, 4):
          raise Error("only 1, 2, or 4 channels supported")
      self._nchannels = nchannels
  
imports: from collections import namedtuple
  import warnings
label_desc: Use image node_id 6 for calling the Au_write obj's underlying member method code with example usage: obj.setnchannels(nchannels) without return types