yggdryl Python bindings

import os
from decimal import Decimal

import pyarrow as pa

from yggdryl import DataType, Field, MediaType, MimeType, Uri

price = DataType.decimal("18", 4)
clock = DataType.time("microseconds")
text = DataType(str)
field = Field("price", price, nullable=False)
field.set_comment("closing price")
field.set_parquet_field_id(17)
field.set_location("s3://warehouse/bars/data.arrow")
field.set_property("postgres", "type", "numeric(18,4)")
scalar = field.arrow_scalar(Decimal("12.5000"))
file = Uri.from_path(r"C:\data\prices.arrow")
encoded = Uri("https://example.test/prices.csv.gz")

assert str(price) == "decimal128(18,4)"
assert str(clock) == "time64(us)"
assert text == DataType("utf8")
assert field.into_arrow().name == "price"
assert field.parquet_field_id == 17
assert field["PARQUET:field_id"] == "17"
assert field.location.scheme == "s3"
assert field.get_property("postgres", "type") == "numeric(18,4)"
assert scalar == pa.scalar(Decimal("12.5000"), type=pa.decimal128(18, 4))
assert str(file) == "file:///C:/data/prices.arrow"
assert os.fspath(file) == "C:/data/prices.arrow"
assert encoded.media_type.base == MimeType("text/csv")
encoded.set_media_type(
    MediaType.from_parts(MimeType("application/json"), [MimeType("application/gzip")])
)
assert encoded.file_name == "prices.json.gz"

The package provides native Python views over Yggdryl's DataType, Field, MimeType, MediaType, Uri, Url, and Urn, plus the @scalar decorator for defining schemas with standard-library dataclasses. Parsing, validation, Arrow conversion, ordering, stable hashing, and path normalization remain owned by Rust. Python 3.10 and PyArrow 18 are the minimum supported versions; 15 supplied the generic Arrow C-stream reader boundary, and 18 is where the run-end-encoded map and extension-type scalar paths became correct. DataType.arrow_scalar(value, *, safe=True) builds a Scalar of the projected physical type. Field.arrow_scalar adds top-level nullability enforcement and returns an already matching Scalar by identity; safe=False explicitly requests PyArrow's unsafe cast rules. Conversion from arbitrary Python objects into a PyArrow Scalar is Python-specific; native scalar validation and materialization are shared through the default-enabled core yggdryl::arrow runtime.

from yggdryl import Field, MediaType, MimeType

media = MediaType.from_parts(MimeType.CSV, [MimeType.GZIP, MimeType.ZSTD])
field = Field(
    "payload",
    "binary",
    metadata={"HTTPS:Content-Type": "text/csv; charset=utf-8"},
)
field.set_media_type(media)

assert field.mime_type == MimeType.CSV
assert field.content_encoding == "gzip, zstd"
assert field.get("HTTPS:CONTENT-TYPE") == "text/csv"

MimeType exposes the complete native known vocabulary as immutable class constants and accepts custom validated MIME names. MediaType() defaults to octet-stream, consumes iterable encodings once, and returns a detached tuple from encodings; it is mutable until first hashed. Hashing locks that wrapper, and a copy is an independent mutable value. URI, URL, and URN values use the same rule. Field HTTP and HTTPS input shares canonical lowercase http:* Arrow metadata. Raw header properties retain parameters, while typed MIME/media, unsigned content length, and absolute HTTP Location accessors validate without a binding-side parser. Pair media updates are atomic and cache-aware. Hashing a Field likewise locks every equality-affecting field and metadata mutation on that wrapper; copies and pickle round-trips are independent values.

Precise Arrow layout can stay beside the logical Python annotation. Reserved Annotated options work as (key, value) pairs or entries in one mapping:

from decimal import Decimal
from typing import Annotated

import pyarrow as pa
from yggdryl import Field

price = Field.from_pyhint(
    "price",
    Annotated[
        Decimal,
        ("arrow_type", pa.decimal128(9, 0)),
        {"nullable": False, "metadata": {"unit": "EUR"}, "id": 7},
    ],
)

assert price.into_arrow().type == pa.decimal128(9, 0)
assert price.parquet_field_id == 7

from yggdryl import Field, types
from yggdryl.types import Int32Field, ListField

trade_id: Int32Field = types.int32("trade_id", nullable=False)
tags: ListField[str] = types.list("tags", types.utf8("item"))

assert type(trade_id) is Field
assert tags.dtype.kind == "list"
assert trade_id.show_diff(trade_id) == "✓ equal"

The categorized yggdryl.types package covers every native datatype variant. Its aliases preserve kind/value information for static typing while factories return the same generic native Field. equals(..., with_metadata=False) can ignore metadata recursively; show_diffs returns readable UTF-8 difference lines and show_diff joins them.

from decimal import Decimal

from yggdryl import scalar
from yggdryl.text import toml

@scalar
class Order:
    order_id: int
    price: Decimal

order = Order(42, Decimal("12.50"))
payload = toml.dumps(order)  # ordinary UTF-8 TOML bytes

assert Order.field().name == "Order"
assert toml.loads(payload, cls=Order) == order

yggdryl.text.json, yggdryl.text.toml, and yggdryl.text.yaml expose byte-first dumps/loads plus declared os.PathLike and typed text/binary file-object dump/load. A source str is always document content; use pathlib.Path to name a source location. String destinations remain paths because output has no content/path ambiguity. JSON Lines and YAML also expose document-stream dump_all/load_all; TOML is deliberately one document. String content uses the borrowed native text path; paths and named or explicitly formatted I/O redirect to the native reader/writer paths without staging a whole encoded document. For load_all, Python supplies only its read(size)/readline(size) protocol: the owning Rust iterator decides JSON Lines and YAML document boundaries, enforces cumulative limits, and reports core byte offsets. It reads lazily under one bounded parser window, leaves the caller-owned stream open, and is fused after its first read or parse failure. A document carries shapes, never class names: a set reads back as a list and a uuid.UUID as its text, and a class is constructed only through an explicit target such as cls=.

import pyarrow as pa

from yggdryl import Field, field

trade_field = Field.from_arrow_schema(
    pa.schema([
        pa.field("trade_id", pa.uint32(), nullable=False),
        pa.field("tags", pa.list_(pa.string()), nullable=False),
    ]),
    name="Trade",
)
Trade = trade_field.into_dataclass()

trade = Trade(trade_id=1, tags=["new"])

assert field(Trade) is trade_field
assert Trade.field() is trade_field
assert Trade.field().into_arrow_schema().field("trade_id").type == pa.uint32()

Arrow schemas import through the native Field, preserving exact physical widths, metadata, dictionary state, and nested layout. into_dataclass() builds a normal dataclass whose cached static field() result is that native shape; it does not inject row conversion, codec, or Arrow methods into the class.

Use cached Class.field() for decorated dataclasses and field(value) for the general conversion funnel.

DataType.cast_arrow_array and Field.cast_arrow_array use the native Arrow kernel plan; their cast_arrow_batch forms reconcile Struct columns by ASCII-case-insensitive name, target order, and Field null/default policy. Readers and writers continue to exchange pyarrow.RecordBatchReader values; class declarations remain schema definitions rather than a second row I/O surface.

Record writes name both their Python representation and intent: overwrite_arrow_reader, append_arrow_table, merge_arrow_batch, and the corresponding *_records, pandas, and polars adapters all redirect to the same streamed Rust pipeline. Every call takes one keyword-only options= value. Set options.commit_row_size = N to publish each complete group of N incoming rows plus the final remainder; leave it as None for one publication after successful end of input. A later failure leaves completed groups visible by design, and zero is rejected before a one-shot Python input is inspected.

For configured intent, the same representations expose write_* with the canonical (input, mode, *, options=None) order. mode is required and is one of "overwrite", "append", or "merge"; it is validated before the input is exported or iterated. is_io() reports the general byte/record capability, while lazy row_size and column_size read whole-media dimensions from native format metadata and cache them only while the handle is open.

DataType(value) infers native wrappers, datatype expression strings, PyArrow datatypes, and Python annotations such as str or list[int]. DataType.decimal(precision, scale=0) also accepts integer-like objects and base-10 numeric strings, selecting Decimal128 through precision 38 and Decimal256 through precision 76. DataType.time(unit) accepts the shared native unit aliases and selects Time32 for seconds/milliseconds or Time64 for microseconds/nanoseconds. Scalar exposes checked native arithmetic through add, subtract, multiply, divide, remainder, negate, and absolute, plus Python's matching operators (including reflected operators and abs). Python-native operands are inferred once at the boundary; overflow, zero division, inexact decimal division, and invalid operand kinds retain distinct Python errors. Expression uses the same arithmetic names and operators to build native trees. Strings remain expression grammar ("price" names a column and "'fee'" is a literal); every non-string Python operand is inferred as one native Scalar, and reflected operators preserve left-to-right order. Avro schemas compare, order, and hash by their complete retained native schema identity; fingerprint() remains the separate Parsing Canonical Form identity that intentionally omits annotations. Decoded Avro containers and immutable Iceberg metadata values use the core's complete equality, ordering, and stable hash identities, with exact copy, repr, and pickle round-trips. Iceberg ScanPlan is a self-contained five-count report, so it supports the same value protocols without retaining a table or executable scan. IcebergOptions is mutable until first hashed; hashing locks every setter, while copied and unpickled options are independent unlocked values. Lazy Avro blocks, bound expressions/statements, and generic RecordOptions deliberately remain unhashable because the core defines no complete canonical value identity for their operational state. Bare DataType.variant() is the self-describing semi-structured Variant datatype; DataType.variant(fields) stays the dense-union sugar building the canonical dense Union with sequential native type IDs - the parenthesis disambiguates. types.variant builds the bare Variant field, types.dense_union the union one, and explicit types.union remains available for custom IDs or sparse layout.

Start with the Python guide and the field classes guide.