redis/redis-py · error · DataError

``count`` is required when ``mode`` or ``ordering`` is set

Error message

``count`` is required when ``mode`` or ``ordering`` is set

What it means

Raised as a `DataError` by `lmovem()` (redis/commands/core.py:3671) when `count` is `None` but `mode` or `ordering` is supplied. LMOVEM's multi-element mode is only meaningful together with a count; specifying mode/ordering without a count is rejected.

Solutions

1. When you set `mode` or `ordering`, also pass `count` (a positive int).
2. Drop `mode`/`ordering` for single-element moves (no count).
3. Treat count, mode, and ordering as a single resolved group before calling.

Example fix

// before
r.lmovem('src', 'dst', mode='EXACTLY')
// after
r.lmovem('src', 'dst', count=3, mode='EXACTLY', ordering='BULK')

if count is None and (mode is not None or ordering is not None):
    raise ValueError('lmovem: count is required when mode/ordering is set')
r.lmovem('a', 'b', count=count, mode=mode, ordering=ordering)

When it happens

Trigger: `r.lmovem('a', 'b', mode='EXACTLY')`, `r.lmovem('a', 'b', ordering='BULK')`, or any LMOVEM call that sets mode/ordering but omits count.

Common situations: Building kwargs conditionally and setting mode/ordering in a branch that forgot count; assuming defaults fill in count; experimental API (LMOVEM is new).

Related errors

• ``ordering`` (OBO or BULK) is required when ``count`` is set
• bit must be 0 or 1
• Both start and end must be specified
• ``byfloat`` and ``byint`` are mutually exclusive.
• ``enx`` requires one of ``ex``, ``px``, ``exat``, or…

AI-assisted analysis of redis/redis-py@6a6b581b48 (2026-08-10). Data as JSON: /api/errors/2cd86443d1a4b1a8. Report an issue: GitHub.

Appendix: source

Thrown at redis/commands/core.py:3672

        ``LEFT`` (head) or ``RIGHT`` (tail).

        When ``count`` is given, ``mode`` selects how many elements to move:
        ``COUNT`` (the default) moves up to ``count`` elements, while
        ``EXACTLY`` moves exactly ``count`` elements or nothing at all. When
        ``count`` is not given a single element is moved.

        ``ordering`` controls the order at the destination: ``OBO`` pushes each
        element as it is popped (reversing block order, stack semantics) while
        ``BULK`` preserves the original relative order (queue semantics). It is
        required whenever ``count`` is given.

        Returns the array of moved elements, or ``None`` if nothing was moved.

        For more information, see https://redis.io/commands/lmovem
        """
        if count is None:
            if mode is not None or ordering is not None:
                raise DataError(
                    "``count`` is required when ``mode`` or ``ordering`` is set"
                )
        elif ordering is None:
            raise DataError(
                "``ordering`` (OBO or BULK) is required when ``count`` is set"
            )
        pieces: list[EncodableT] = [first_list, second_list, src, dest]
        if count is not None:
            pieces.extend([mode or "COUNT", count, ordering])
        return self.execute_command("LMOVEM", *pieces)

    @overload
    def blmovem(
        self: SyncClientProtocol,
        first_list: str,
        second_list: str,
        timeout: float,
        src: str = "LEFT",

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