jax-ml/jax · error · ValueError

Character '.' must be used inside ellipsis '...'

Error message

Character '.' must be used inside ellipsis '...'

What it means

Raised while normalizing a sharding rule: the parser first rewrites '...' into a BATCHING token; any remaining '.' in the rule is a stray character that is not part of an ellipsis and is therefore rejected.

Solutions

1. Fix the ellipsis to be exactly '...' or remove the stray dot
2. Ensure factor names contain no '.' characters

Example fix

# before
rule = '..i,j->j'
# after
rule = '...i,j->j'

assert '..' not in rule.replace('...', ''), 'dots only allowed inside ...'

def dots_only_in_ellipsis(rule: str) -> bool:
    return '.' not in rule.replace('...', '')

When it happens

Trigger: Rule like 'i.j->j', '..i->i' (two dots), or '...i.j' with a stray dot.

Common situations: Typos when typing ellipsis (two or four dots); einsum habits where '.' never appears; filesystem-like names in factor names.

Related errors

• Brackets are not balanced
• Brackets are not balanced in rule
• Brackets should contain at least two factors
• Compound factors should be one level, nested brackets are…
• Factor names have to start with a letter, but got

AI-assisted analysis of jax-ml/jax@1e1c6a8fc0 (2026-08-27). Data as JSON: /api/errors/71fad57962c3ca35. Report an issue: GitHub.

Appendix: source

Thrown at jax/_src/custom_partitioning_sharding_rule.py:347

    permutation_factors: A tuple of factors that are permutation factors.
    **factor_sizes: The optional factor sizes.

  Raises:
    ValueError: If there is any problem with the rule or factor_sizes.
  """
  if not isinstance(rule, str):
    raise TypeError(f"rule must be a str, but got {type(rule)}")
  if not all(isinstance(size, int) for size in factor_sizes.values()):
    raise TypeError(
        f"factor_sizes must be a dict of str to int, but got {factor_sizes}")

  # Replace ... with a single char to simplify parsing.
  if BATCHING in rule:
    raise ValueError(f"Unknown character '{BATCHING}'")
  if "." in rule:
    rule = rule.replace("...", BATCHING)
    if "." in rule:
      raise ValueError("Character '.' must be used inside ellipsis '...'")

  try:
    operands, results = rule.split("->")
  except ValueError as e:
    raise ValueError(f"There is no -> in rule: '{rule}'") from e

  operand_mappings = _parse_values(operands)
  result_mappings = _parse_values(results)
  return SdyShardingRule(operand_mappings, result_mappings,
                         reduction_factors=reduction_factors,
                         need_replication_factors=need_replication_factors,
                         permutation_factors=permutation_factors,
                         **factor_sizes)


def sdy_sharding_rule_to_mlir(
  rule: SdyShardingRule,
  operand_types: list[ir.Type],

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