pathwaycom/pathway · error · ValueError

Schema must be specified.

Error message

Schema must be specified.

What it means

Error "Schema must be specified." thrown in pathwaycom/pathway.

Source

Thrown at python/pathway/io/_utils.py:255

        # the primary key and None. If any (including empty) set of keys if provided,
        # then it will be used to compute the primary key.
        key_field_names=schema.primary_key_columns(),
        value_fields=value_fields,
    )


def assert_schema_not_none(
    schema: type[Schema] | None,
    data_format_type: str | None = None,
) -> type[Schema]:
    if schema is None:
        if data_format_type == "dsv":
            raise ValueError(
                "Schema must be specified. "
                "Consider using `pw.schema_from_csv` for generating schema from a CSV file"
            )
        else:
            raise ValueError("Schema must be specified.")
    else:
        return schema


class PlaintextKeySchema(pw.Schema):
    key: str


class RawKeySchema(pw.Schema):
    key: bytes


def construct_raw_data_schema_by_flags(
    *, with_native_record_key: bool, parse_utf8: bool, with_metadata: bool
) -> type[pw.Schema]:
    Schema: Any
    if parse_utf8:
        Schema = PlaintextDataSchema

View on GitHub (pinned to fa2f74a464)

Solutions

1. Provide the schema explicitly via the schema parameter of the read call.

Example fix

pw.io.jsonlines.read(path, schema=MySchema)

When it happens

Trigger: Thrown at python/pathway/io/_utils.py:255 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of pathwaycom/pathway@fa2f74a464 (2026-08-15). Data as JSON: /api/errors/e8b8f8faba931051. Report an issue: GitHub.