polspec

Declare a Polars schema once. Generate data that matches it, and validate data against it — from the same declaration.

Early alpha. The API, the YAML format, and the exact values a given seed produces are all still moving. See Roadmap and stability before depending on any of it.

import polars as pl
from polspec import ColSpec, FrameSpec

class Orders(FrameSpec):
    order_id = ColSpec(pl.Int64, bounds=(1, None), unique=True)
    status   = ColSpec(pl.Enum(["NEW", "PAID", "SHIPPED"]))
    total    = ColSpec(pl.Float64, bounds=(0.0, None))
    placed   = ColSpec(pl.Date, nullable=True)

df = Orders.generate(1_000_000, seed=42)   # a million rows in well under a second
Orders.validate(df)                        # raises ValidationError on any breach

A validation library tells you when production data drifted. A fixture library gives you something to test against. Keeping both behind one declaration means the fixtures and the contract cannot quietly disagree — and where they still can, it is written down in Known limitations, each backed by a test that fails the moment it stops being true.

The generator is a Rust extension that fills columns in parallel; validate() compiles every check across every column into a single Polars aggregation, so validating a wide table costs about the same as a narrow one. Numbers, and comparisons to NumPy and hand-written fixtures, are in Comparison.

Install

uv add polspec           # preferred
pip install polspec      # alternative
uv add "polspec[arrow]"  # extra: PyArrow for the Parquet/IPC sinks

Wheels are published for Linux (x86_64, aarch64), macOS (Intel and Apple silicon) and Windows (x86_64), so using polspec needs no Rust toolchain. Building from a checkout is covered in CONTRIBUTING.md.

Documentation

Full docs: maxwellb13.github.io/polspec

• Tutorial — Getting started · Related tables
• How-to — Declare columns · Constraints · Generate · Validate · Specs as files · Command line
• Reference — API · Errors and findings
• Explanation — Architecture · Generation and validation · Known limitations · Roadmap

Development

uv run pytest
uv run ruff check . && uv run ruff format --check .
cargo test && cargo clippy --all-targets -- -D warnings
uv run --group docs zensical build --strict
uv run python examples/related_specs.py

uv run --group bench python benchmarks/bench_generate.py runs the generator benchmark. See CONTRIBUTING.md for conventions and the release process, and CHANGELOG.md for what changed.

License

MIT.