openai/openai-python · error · TypeError

Unexpected, list delta entry `index` value is not an integer

Error message

Unexpected, list delta entry `index` value is not an integer; {index}

What it means

Raised inside accumulate_delta when a list delta entry's index value is present but not an int (e.g. a string '0' or None). The merger indexes Python lists with it, so a non-integer index is rejected with this TypeError showing the bad value.

Source

Thrown at src/openai/lib/streaming/_assistants.py:1027

            acc_value = accumulate_delta(acc_value, delta_value)
        elif is_list(acc_value) and is_list(delta_value):
            # for lists of non-dictionary items we'll only ever get new entries
            # in the array, existing entries will never be changed
            if all(isinstance(x, (str, int, float)) for x in acc_value):
                acc_value.extend(delta_value)
                continue

            for delta_entry in delta_value:
                if not is_dict(delta_entry):
                    raise TypeError(f"Unexpected list delta entry is not a dictionary: {delta_entry}")

                try:
                    index = delta_entry["index"]
                except KeyError as exc:
                    raise RuntimeError(f"Expected list delta entry to have an `index` key; {delta_entry}") from exc

                if not isinstance(index, int):
                    raise TypeError(f"Unexpected, list delta entry `index` value is not an integer; {index}")

                try:
                    acc_entry = acc_value[index]
                except IndexError:
                    acc_value.insert(index, delta_entry)
                else:
                    if not is_dict(acc_entry):
                        raise TypeError("not handled yet")

                    acc_value[index] = accumulate_delta(acc_entry, delta_entry)

        acc[key] = acc_value

    return acc

View on GitHub (pinned to 9917c6e28e)

Solutions

Ensure index is a plain int (json.loads yields int for JSON numbers - check for manual coercion)
Upgrade the SDK to match the current API schema
Validate/normalize delta entries before accumulation in custom pipelines
Catch TypeError and replace the accumulated list as a fallback

Example fix

# before
entry = {"index": "0", "text": "hi"}

# after
entry = {"index": 0, "text": "hi"}

Defensive patterns

Strategy: validation

Validate before calling

def entries_have_int_index(entries) -> bool:
    return all(
        isinstance(e, dict) and type(e.get("index")) is int for e in entries
    )

Type guard

null

Try / catch

try:
    acc = accumulate_delta(acc, delta)
except TypeError:
    acc[key] = copy.deepcopy(delta)

Prevention

Normalize index to int before accumulating custom deltas
Watch for middleware that stringifies JSON values
Upgrade SDK when API serialization changes

When it happens

Trigger: Delta payloads where index is serialized as a string or null; schema changes in beta streaming endpoints; test fixtures using JSON-ish typed indices.

Common situations: Version mismatch between SDK accumulator strictness and API serialization; middleware/proxies rewriting JSON; handcrafted delta dicts in unit tests.

Related errors

AI-assisted analysis of openai/openai-python@9917c6e28e (2026-08-28). Data as JSON: /api/errors/48547f7f3dd3a332. Report an issue: GitHub.