docs: def check_valid_channel(self,
                              channel,
                              conda_url='https://conda.anaconda.org'):
          """Check if channel is valid."""
          if channel.startswith('https://') or channel.startswith('http://'):
              url = channel
          else:
              url = "{0}/{1}".format(conda_url, channel)
  
          if url[-1] == '/':
              url = url[:-1]
          plat = self.conda_platform()
          repodata_url = "{0}/{1}/{2}".format(url, plat, 'repodata.json')
          worker = self.download_is_valid_url(repodata_url)
          worker.url = url
          return worker