code: def truncate_to_issuer(self, cert):
          
  
          issuer_index = None
          for index, entry in enumerate(self):
              if entry.subject == cert.issuer:
                  if entry.key_identifier and cert.authority_key_identifier:
                      if entry.key_identifier == cert.authority_key_identifier:
                          issuer_index = index
                          break
                  else:
                      issuer_index = index
                      break
  
          if issuer_index is None:
              raise LookupError('Unable to find the issuer of the certificate specified')
  
          while len(self) > issuer_index + 1:
              self.pop()
  
          return self
docs: Remove all certificates in the path after the issuer of the cert
          specified, as defined by this path
  
          :param cert:
              An asn1crypto.x509.Certificate object to find the issuer of
  
          :raises:
              LookupError - when the issuer of the certificate could not be found
  
          :return:
              The current ValidationPath object, for chaining