docs: def proxy_servers(self):
          """
          Return the proxy servers available.
  
          First env variables will be searched and updated with values from
          condarc config file.
          """
          proxy_servers = {}
          if self._load_rc_func is None:
              return proxy_servers
          else:
              HTTP_PROXY = os.environ.get('HTTP_PROXY')
              HTTPS_PROXY = os.environ.get('HTTPS_PROXY')
  
              if HTTP_PROXY:
                  proxy_servers['http'] = HTTP_PROXY
  
              if HTTPS_PROXY:
                  proxy_servers['https'] = HTTPS_PROXY
  
              proxy_servers_conf = self._load_rc_func().get('proxy_servers', {})
              proxy_servers.update(proxy_servers_conf)
  
              return proxy_servers