pathwaycom/pathway · error · TypeError

Got unexpected keyword argument 'topic_name'. pw.io.kafka.re

Error message

Got unexpected keyword argument 'topic_name'. pw.io.kafka.read uses 'topic' (the corresponding parameter in pw.io.kafka.write is 'topic_name'). Please rename 'topic_name=' to 'topic='.

What it means

pw.io.kafka.read names its topic parameter 'topic', while pw.io.kafka.write names it 'topic_name'. Because **kwargs is part of read's signature (for deprecated aliases), passing topic_name=... would normally be silently ignored; Pathway detects this specific typo and raises TypeError telling you to rename it.

Source

Thrown at python/pathway/io/kafka/__init__.py:317

    if (
        start_from_timestamp_ms is not None
        and user_offset_reset is not None
        and user_offset_reset not in _START_FROM_BEGINNING_ALIASES
    ):
        warnings.warn(
            "'auto.offset.reset' is overridden to 'earliest' whenever "
            "'start_from_timestamp_ms' is set, so the seek can fall back "
            f"to the start of the partition. Your value "
            f"{user_offset_reset!r} is being ignored.",
            stacklevel=_stacklevel + 4,
        )

    # Distinguish "missing topic" from "explicitly empty topic" — the former
    # is a user typo (rename to 'topic='), the latter is an invalid value
    # that Kafka itself would reject with a less actionable error.
    if topic is None:
        if "topic_name" in kwargs:
            raise TypeError(
                "Got unexpected keyword argument 'topic_name'. "
                "pw.io.kafka.read uses 'topic' (the corresponding parameter "
                "in pw.io.kafka.write is 'topic_name'). Please rename "
                "'topic_name=' to 'topic='."
            )
        topic_names = kwargs.pop("topic_names", None)
        if not topic_names:
            raise ValueError("Missing topic name specification")
        if isinstance(topic_names, str):
            warnings.warn(
                "'topic_names' is deprecated; please use 'topic' instead.",
                DeprecationWarning,
                stacklevel=_stacklevel + 4,
            )
            topic = topic_names
        elif isinstance(topic_names, (list, tuple)):
            warnings.warn(
                "'topic_names' is deprecated; please use 'topic' instead. "

View on GitHub (pinned to fa2f74a464)

Solutions

1. Rename the keyword: use topic='test-topic' in pw.io.kafka.read.
2. Keep read and write calls in separate helper functions with their own explicit parameter names rather than sharing one kwargs dict.

Example fix

# before
t = pw.io.kafka.read(rdkafka_settings, topic_name="test-topic")
# after
t = pw.io.kafka.read(rdkafka_settings, topic="test-topic")

def normalize_read_kwargs(kwargs: dict) -> dict:
    kwargs = dict(kwargs)
    if "topic_name" in kwargs and "topic" not in kwargs:
        kwargs["topic"] = kwargs.pop("topic_name")  # read() uses 'topic'
    return kwargs

t = pw.io.kafka.read(rdkafka_settings, **normalize_read_kwargs(user_kwargs))

When it happens

Trigger: pw.io.kafka.read(rdkafka_settings, topic_name='test-topic') — read() receives no 'topic' positional/keyword and finds 'topic_name' in kwargs.

Common situations: Copy-pasting a write() call and changing only the table argument; writing a helper that forwards the same kwargs dict to both read and write; muscle memory from the write API.

Related errors

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

AI-assisted analysis of pathwaycom/pathway@fa2f74a464 (2026-08-15). Data as JSON: /api/errors/d22c1add2207f236. Report an issue: GitHub.