code: def _is_valid_channel(self, channel,
                            conda_url='https://conda.anaconda.org'):
          
          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_api.get_platform()
          repodata_url = "{0}/{1}/{2}".format(url, plat, 'repodata.json')
  
          try:
              r = requests.head(repodata_url, proxies=self.proxy_servers)
              value = r.status_code in [200]
          except Exception as error:
              logger.error(str(error))
              value = False
  
          return value
docs: Callback for is_valid_channel.