redis/redis-py · error · DataError

specific_argument can be only keys or strings

Error message

specific_argument can be only keys or strings

What it means

Raised by stralgo() when specific_argument is neither 'keys' nor 'strings'. This parameter tells Redis whether value1/value2 should be treated as key names to look up or as literal string values; any other value is meaningless to the command. It is a DataError.

Solutions

1. Set specific_argument='strings' to compare literal string values, or specific_argument='keys' to compare values stored at those keys.
2. Double-check spelling: it must be exactly 'keys' or 'strings' (plural).

Example fix

# before
client.stralgo('LCS', 'k1', 'k2', specific_argument='key')

# after
client.stralgo('LCS', 'k1', 'k2', specific_argument='keys')

if specific_argument not in ('keys', 'strings'):
    raise ValueError("specific_argument must be 'keys' or 'strings'")
client.stralgo('LCS', v1, v2, specific_argument=specific_argument)

from typing import Literal

def is_valid_specific_arg(s: str) -> bool:
    return s in ('keys', 'strings')

# usage
specific_argument: Literal['keys', 'strings'] = 'strings'

from redis.exceptions import DataError
try:
    client.stralgo('LCS', v1, v2, specific_argument=specific_argument)
except DataError as e:
    if 'specific_argument' in str(e):
        specific_argument = 'strings'
        client.stralgo('LCS', v1, v2, specific_argument=specific_argument)

When it happens

Trigger: Calling client.stralgo('LCS', v1, v2, specific_argument='values'), specific_argument='key', or omitting the default and passing an arbitrary string.

Common situations: Typing 'value' instead of 'strings', or 'key' instead of 'keys'. Confusing whether to pass key names or raw strings.

Related errors

• The supported algorithms are
• len and idx cannot be provided together.
• ACL LOG count must be an integer
• bit must be 0 or 1
• Both start and end must be specified

AI-assisted analysis of redis/redis-py@6a6b581b48 (2026-08-10). Data as JSON: /api/errors/c174994ed53db774. Report an issue: GitHub.

Appendix: source

Thrown at redis/commands/core.py:4622

        ``value1`` and ``value2`` Can be two strings or two keys
        ``specific_argument`` Specifying if the arguments to the algorithm
        will be keys or strings. strings is the default.
        ``len`` Returns just the len of the match.
        ``idx`` Returns the match positions in each string.
        ``minmatchlen`` Restrict the list of matches to the ones of a given
        minimal length. Can be provided only when ``idx`` set to True.
        ``withmatchlen`` Returns the matches with the len of the match.
        Can be provided only when ``idx`` set to True.

        For more information, see https://redis.io/commands/stralgo
        """
        # check validity
        supported_algo = ["LCS"]
        if algo not in supported_algo:
            supported_algos_str = ", ".join(supported_algo)
            raise DataError(f"The supported algorithms are: {supported_algos_str}")
        if specific_argument not in ["keys", "strings"]:
            raise DataError("specific_argument can be only keys or strings")
        if len and idx:
            raise DataError("len and idx cannot be provided together.")

        pieces: list[EncodableT] = [algo, specific_argument.upper(), value1, value2]
        if len:
            pieces.append(b"LEN")
        if idx:
            pieces.append(b"IDX")
        try:
            int(minmatchlen)
            pieces.extend([b"MINMATCHLEN", minmatchlen])
        except TypeError:
            pass
        if withmatchlen:
            pieces.append(b"WITHMATCHLEN")

        return self.execute_command(
            "STRALGO",

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