pathwaycom/pathway · error · ValueError

'read_only_new=True' together with mode='static' is self-con

Error message

'read_only_new=True' together with mode='static' is self-contradictory: 'read_only_new' starts the consumer at the end of the partition, so the static reader has nothing to consume. Pick one — drop 'read_only_new=True' or use 'mode="streaming"' (the default).

What it means

In pw.io.kafka.simple_read, read_only_new=True sets auto.offset.reset='end' so the consumer starts at the newest messages, while mode='static' reads only what exists at snapshot time. The combination would find nothing to consume, so Pathway rejects it as self-contradictory with an explicit ValueError.

Source

Thrown at python/pathway/io/kafka/__init__.py:502

    following way:

    >>> import pathway as pw
    >>> t = pw.io.kafka.simple_read("localhost:9092", "test-topic")
    """

    forbidden_kwargs = ("rdkafka_settings", "_stacklevel")
    for forbidden in forbidden_kwargs:
        if forbidden in kwargs:
            raise TypeError(
                f"'simple_read' does not accept {forbidden!r}. "
                "If you need to customize the rdkafka settings (auth, TLS, "
                "consumer group, etc.) use 'pw.io.kafka.read' directly; "
                "'simple_read' is a thin wrapper that builds these settings "
                "itself."
            )

    if read_only_new and kwargs.get("mode") == "static":
        raise ValueError(
            "'read_only_new=True' together with mode='static' is "
            "self-contradictory: 'read_only_new' starts the consumer at the "
            "end of the partition, so the static reader has nothing to "
            "consume. Pick one — drop 'read_only_new=True' or use "
            "'mode=\"streaming\"' (the default)."
        )
    if read_only_new and kwargs.get("start_from_timestamp_ms") is not None:
        raise ValueError(
            "'read_only_new=True' and 'start_from_timestamp_ms' both control "
            "the starting position and conflict. Pick one — drop "
            "'read_only_new=True' if you want to start from the timestamp, "
            "or drop 'start_from_timestamp_ms' if you want to start from "
            "the end."
        )

    rdkafka_settings = {
        "bootstrap.servers": server,
        "group.id": str(uuid.uuid4()),

View on GitHub (pinned to fa2f74a464)

Solutions

1. Drop read_only_new=True if you want a static snapshot-style read from the beginning.
2. Or switch to mode='streaming' (the default) if you want to process only newly arriving messages.
3. Remember static mode implies a bounded read; streaming mode with read_only_new gives a live tail of the topic.

Example fix

# before
t = pw.io.kafka.simple_read("localhost:9092", "test-topic", read_only_new=True, mode="static")
# after
t = pw.io.kafka.simple_read("localhost:9092", "test-topic", read_only_new=True)  # mode="streaming" default

if read_only_new and mode == "static":
    raise SystemExit(
        "read_only_new=True needs streaming mode; drop it or use mode='streaming'"
    )

t = pw.io.kafka.simple_read("localhost:9092", "test-topic", read_only_new=read_only_new, mode=mode)

def compatible_simple_read_opts(read_only_new: bool, mode: str) -> bool:
    return not (read_only_new and mode == "static")

When it happens

Trigger: pw.io.kafka.simple_read('localhost:9092', 'test-topic', read_only_new=True, mode='static'). The default mode is 'streaming', where read_only_new is valid.

Common situations: Adding read_only_new=True to an existing static-mode pipeline expecting 'only new data going forward'; copy-pasting flags between examples without reconciling mode semantics.

Related errors

• Got unexpected keyword argument 'topic_name'. pw.io.kafka.re
• Missing topic name specification
• 'topic_names' must be a str or a list of str; got {type(topi
• 'topic' must be a non-empty string; got an empty list. Kafka
• 'simple_read' does not accept {forbidden!r}. If you need to

AI-assisted analysis of pathwaycom/pathway@fa2f74a464 (2026-08-15). Data as JSON: /api/errors/a38f6d2970340f37. Report an issue: GitHub.