unslothai/unsloth · error · ValueError

seeds must be a non-empty list of integers

Error message

seeds must be a non-empty list of integers

What it means

When a seeds parameter is provided it must be a non-empty list of integers. seeds=[] (empty list) is rejected here; None means 'no seeds given' and is valid. Note the element-type check is not strict at this line — values are coerced with int(s) afterwards, and out-of-range values are caught by a separate check — but non-integer-coercible elements will raise on the int() conversion.

Source

Thrown at studio/backend/core/inference/diffusion_batched.py:67

    """The per-image ``(prompt, seed)`` jobs plus the base seed for this call.

    - ``prompts`` (list): one image per prompt. With ``seeds`` too, lengths must
      match (seed i drives prompt i); without, seeds derive from the base.
    - ``seeds`` (list) alone: one image per seed, all with ``prompt``.
    - neither: ``batch_size`` images of ``prompt`` with derived seeds
      base..base+batch_size-1 (each masked JSON-safe).

    ``draw_seed`` supplies a fresh random base when the caller sent none (the
    engine passes a ``torch.Generator`` draw). Raises ``ValueError`` on empty /
    oversized lists, a length mismatch, or an out-of-range seed."""
    if prompts is not None:
        if not prompts or not all(isinstance(p, str) and p.strip() for p in prompts):
            raise ValueError("prompts must be a non-empty list of non-empty strings")
        if len(prompts) > MAX_BATCH_IMAGES:
            raise ValueError(f"prompts supports at most {MAX_BATCH_IMAGES} entries per call")
    if seeds is not None:
        if not seeds:
            raise ValueError("seeds must be a non-empty list of integers")
        if len(seeds) > MAX_BATCH_IMAGES:
            raise ValueError(f"seeds supports at most {MAX_BATCH_IMAGES} entries per call")
        seeds = [int(s) for s in seeds]
        if any(s < 0 or s > SEED_MASK for s in seeds):
            raise ValueError("every seed must be between 0 and 2**53 - 1 (JSON-safe)")
        if prompts is not None and len(seeds) != len(prompts):
            raise ValueError(
                f"prompts and seeds must have the same length "
                f"(got {len(prompts)} prompts, {len(seeds)} seeds)"
            )

    if prompts is not None:
        count = len(prompts)
    elif seeds is not None:
        count = len(seeds)
    else:
        count = max(1, int(batch_size))

View on GitHub (pinned to 203007d190)

Solutions

  1. Send seeds: null (or omit the field) when you have no seeds to pin, instead of an empty list.
  2. Or populate the list with at least one integer seed (0 to 2**53-1).

Example fix

# before
engine.generate(prompt=p, seeds=[])
# after
engine.generate(prompt=p, seeds=None)  # or omit seeds entirely
Defensive patterns

Strategy: validation

Validate before calling

def valid_seeds_shape(seeds) -> bool:
    return seeds is None or (isinstance(seeds, list) and len(seeds) > 0)

Type guard

def is_valid_seed_list(v) -> bool:
    return v is None or (isinstance(v, list) and len(v) > 0)

Try / catch

try:
    out = engine.generate(prompt=p, seeds=seeds)
except ValueError as e:
    if "seeds must be a non-empty list" in str(e):
        out = engine.generate(prompt=p, seeds=None)  # let the engine draw
    else:
        raise

Prevention

When it happens

Trigger: Calling generate with seeds=[] — commonly produced by client-side code that builds the seeds list conditionally and ends up empty instead of None.

Common situations: seeds = [compute_seed() for x in items] where items is empty; UI 'lock seed' features sending an empty array when no seeds are locked; JSON payloads with "seeds": [].

Related errors

AI-assisted analysis of unslothai/unsloth@203007d190 (2026-08-15). Data as JSON: /api/errors/a65539c9207669cc. Report an issue: GitHub.