redis/redis-py · error · ConnectionError

protocol must be an integer

Error message

protocol must be an integer

What it means

ConnectionError from the async Connection constructor (redis/asyncio/connection.py:701) when int(protocol) raises ValueError - i.e. protocol is a non-numeric string. The protocol argument must be coercible to an integer (2 or 3). A non-numeric value is rejected early rather than failing later during HELLO negotiation.

Solutions

  1. Pass an integer: Redis(protocol=3)
  2. Validate/convert config strings to int before passing: int(os.environ['REDIS_PROTOCOL'])
  3. Leave protocol unset to use the library default (DEFAULT_RESP_VERSION=3)

Example fix

// before
Redis(protocol=os.environ.get('REDIS_PROTOCOL', '3'))
// after
Redis(protocol=int(os.environ.get('REDIS_PROTOCOL', 3)))
Defensive patterns

Strategy: validation

Validate before calling

try:
    protocol = int(protocol)
except (TypeError, ValueError):
    protocol = 3  # or raise a clear config error

Prevention

When it happens

Trigger: `Redis(protocol='three')`, `Redis(protocol='2.7')` (float-string), or any protocol value that int() cannot parse.

Common situations: Reading protocol from an env var or config file as a string typo; passing the string form of the version.

Related errors

AI-assisted analysis of redis/redis-py@6a6b581b48 (2026-08-10). Data as JSON: /api/errors/944430898c6d862f. Report an issue: GitHub.

Appendix: source

Thrown at redis/asyncio/connection.py:701

        self.health_check_interval = health_check_interval
        self.next_health_check: float = -1
        self.encoder = encoder_class(encoding, encoding_errors, decode_responses)
        self.redis_connect_func = redis_connect_func
        self._reader: Optional[asyncio.StreamReader] = None
        self._writer: Optional[asyncio.StreamWriter] = None
        self._socket_read_size = socket_read_size
        self._active_read_timeout = None
        self._connect_callbacks: List[weakref.WeakMethod[ConnectCallbackT]] = []
        self._buffer_cutoff = 6000
        self._re_auth_token: Optional[TokenInterface] = None
        self._should_reconnect = False

        try:
            p = int(protocol)
        except TypeError:
            p = DEFAULT_RESP_VERSION
        except ValueError:
            raise ConnectionError("protocol must be an integer")
        else:
            if p < 2 or p > 3:
                raise ConnectionError("protocol must be either 2 or 3")
        self.protocol = p
        self.legacy_responses = legacy_responses
        if parser_class != _AsyncHiredisParser:
            # The Python parsers are protocol-specific; hiredis supports both.
            if self.protocol == 3 and parser_class == _AsyncRESP2Parser:
                parser_class = _AsyncRESP3Parser
            elif self.protocol == 2 and parser_class == _AsyncRESP3Parser:
                parser_class = _AsyncRESP2Parser
        self.set_parser(parser_class)

        # HIMPORT client-side state. `himport_registry` is the shared client-level
        # registry (empty if unconfigured) and persists across reconnects.
        self.himport_registry = himport_registry
        self._reset_himport_state()

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