docs: def _extract_subdomain(host):
          """ Returns a subdomain from a host. This host is typically the
          HTTP_HOST request envvar.  If the host is an IP address, `None` is
          returned
  
          :param host: Request's target host
          """
          host = host.split(':')[0]
          # If the host is an IP address, there is no subdomain to extract
          try:
              # Check if the host is an ip address
              socket.inet_aton(host)
          except socket.error:
              # It isn't an IP address, return the subdomain
              return '.'.join(host.split('.')[:-2])