hypercast

match/case over a two-case verdict — the value, or a closed reason plus the exact byte span that offended — with the Rust core linked straight into CPython as a native extension. No dlopen, no ctypes marshalling, no runtime bridge.

Allocation-lean scalar casts — booleans, the full integer family, reals, exact decimals, UUIDs, temporals. The PyO3 extension (hypercast._native) is the backend every wheel ships — a door is an ordinary METH_FASTCALL extension call into a direct Rust call, and the wheel maturin builds is the whole package (the interim ctypes fallback is gone). Python 3.11 is the floor, the oldest version still in upstream support (match/case is the consumption idiom).

Install

pip install hypercast

Real platform-specific wheels, so it lands at native speed with nothing to compile — no compiler needed and no dependencies at all; the PyO3 extension is the package. The wheels are abi3 (abi3-py311), so one per platform covers every CPython from the 3.11 floor up — eight native ones, plus a ninth for Pyodide in the browser (below):

Only wheels are published — there is no sdist. An interpreter none of the wheels matches (a glibc older than 2.28, PyPy, free-threaded CPython) gets No matching distribution found from pip, not a source build.

On Alpine the musl wheel needs nothing beyond the base image — it carries its own copy of libgcc_s — and the whole suite passes on a bare python:3.14-alpine.

Not yet covered: free-threaded (no-GIL) CPython (3.13t/3.14t). An abi3 wheel is ignored by a free-threaded interpreter (it's a genuinely separate ABI, not a compatibility flag), so closing this gap means building and shipping additional version-specific cp313t/cp314t wheels alongside the existing ones, not just a build-flag change. PyO3 itself has supported free-threading (opt-in, gil_used = false) since 0.23; the cleaner long-term fix — PEP 803's abi3t stable ABI, one build covering both GIL and no-GIL — needs Python 3.15+, not yet released. Revisiting once that lands or free-threaded adoption justifies the extra wheel legs. The stance in the code today: the extension module does not declare gil_used = false, so a build from a checkout for a free-threaded interpreter imports with the GIL switched back on (CPython says so in a RuntimeWarning) — correct, just not parallel. And no door releases the GIL: each is tens to hundreds of nanoseconds of pure Rust, less than the handoff would cost.

The package is typed: it ships py.typed and a stub for the extension module, so mypy and pyright see each door's own Success[...] | Fault rather than Any — which is what makes the exhaustiveness check below a real one.

Usage

import hypercast

match hypercast.cast_i32("(1,234)", hypercast.NumFormat.INVARIANT):
    case hypercast.Success(value):
        print("got", value)                       # -1234, accounting negative
    case hypercast.Fault(reason, offset, length):
        print(reason.name, "at byte", offset)

Door names mirror the native ABI (cast_i32, cast_f64, cast_decimal, cast_timestamp, …); inputs are str or bytes, both zero-copy views, and a Fault's span comes back in the caller's own units — byte offsets for bytes, code-point offsets for str — so text[offset:offset + length] slices the offending text back out of whatever you passed, no mapping needed. Exhaustiveness is the type checker's job here — pair the two cases with typing.assert_never under mypy/pyright for the compile-time guarantee the static bindings get natively. Python-flavored fidelity, stated honestly: int is unbounded, so cast_u64 returns the true unsigned value with no bit-pattern games; cast_decimal returns an exact, canonical decimal.Decimal; datetime's resolution is microseconds, so the core's nanoseconds truncate by three digits on the temporal doors — datetime's own ceiling, not the parser's, and said out loud rather than discovered later.

The exhaustiveness check, spelled out — Verdict[int] is Success[int] | Fault, what cast_i32 returns, and the fall-through arm stops type-checking the moment either case above it goes missing (assert_never is in typing on every supported Python):

from typing import assert_never

def describe(verdict: hypercast.Verdict[int]) -> str:
    match verdict:
        case hypercast.Success(value):
            return f"got {value}"                 # value: int
        case hypercast.Fault(reason, offset, length):
            return f"{reason.name} at {offset}"
        case _:
            assert_never(verdict)

The doors

Every door takes the text first — str or bytes — and returns Success(value) or Fault(reason, offset, length):

Nothing about the text is guessed; what a door cannot know from the text, the caller declares, as an IntEnum:

• UnixPrecision — SECONDS, MILLISECONDS, MICROSECONDS, NANOSECONDS: the unit of a Unix-epoch value, never inferred from its magnitude.
• ExcelEpoch — Y1900 (the Windows default, phantom February 29th 1900 included) or Y1904 (the legacy Macintosh system): a workbook-level setting no serial number carries.
• DateOrder — YEAR_MONTH_DAY, MONTH_DAY_YEAR, DAY_MONTH_YEAR: "1/7/2026" is January 7th or July 1st only because the caller said which. Without one, cast_date stays strict ISO.

from hypercast import DateOrder, ExcelEpoch, UnixPrecision

hypercast.cast_unix("1700000000123", UnixPrecision.MILLISECONDS)
# Success(value=datetime.datetime(2023, 11, 14, 22, 13, 20, 123000, tzinfo=datetime.timezone.utc))
hypercast.cast_excel_serial("45000", ExcelEpoch.Y1900)
# Success(value=datetime.datetime(2023, 3, 15, 0, 0, tzinfo=datetime.timezone.utc))
hypercast.cast_date("1/7/2026", DateOrder.DAY_MONTH_YEAR)
# Success(value=datetime.date(2026, 7, 1))
hypercast.cast_datetime("1/7/2026 3:04 PM", DateOrder.MONTH_DAY_YEAR)
# Success(value=datetime.datetime(2026, 1, 7, 15, 4))
hypercast.cast_duration("PT1H30M")
# Success(value=datetime.timedelta(seconds=5400))

A Fault's reason is a CastFailure — EMPTY (nothing there, or only whitespace), MALFORMED (present, but not the target type) or OUT_OF_RANGE (well-formed, outside the target's range) — compared with is. hypercast.optional(verdict) presents an EMPTY fault as None and passes everything else through, for the column where blank means absent:

hypercast.optional(hypercast.cast_i32("   ", hypercast.NumFormat.INVARIANT))    # None
hypercast.optional(hypercast.cast_i32("abc", hypercast.NumFormat.INVARIANT))    # Fault(reason=<CastFailure.MALFORMED: 2>, offset=0, length=1)

Bad data is always a Fault. What raises is a caller's bug: TypeError for an argument of the wrong type (text that is neither str nor bytes, a format that is not a NumFormat), ValueError for a declaration that names no member of its enum or a NumFormat that cannot be (below), OverflowError for an integer too wide for the 32 unsigned bits a flag set or a declaration is. The one exception that is about data: a str holding a lone surrogate has no UTF-8 form, so it is a UnicodeEncodeError before any door runs.

See the repo root README for the receipts and the state of every other language binding.

Declared formats: separators, lenience flags, currency

Every numeric door — the integer family, cast_f32/cast_f64, and cast_decimal — takes a NumFormat: the decimal and group separators, a bitwise OR of the lenience flags (GROUPING, PARENTHESES, EXPONENT, RADIX_PREFIXES, PERCENT, CURRENCY; ALL is all six — SEPARATOR_DETECT is a separator policy, not a lenience, and is opted into separately), and an optional currency symbol. NumFormat.INVARIANT is ./, with every lenience on and no symbol; NumFormat.DETECT is the same with SEPARATOR_DETECT added, so the ./, roles are resolved per input from its structure (1.234.567,89 and 1,234,567.89 both read) and an undecidable one is a MALFORMED fault, never a guess; NumFormat.from_localeconv() bridges locale.localeconv() — decimal_point, thousands_sep, and currency_symbol. A format is immutable and reads back through decimal_sep, group_sep, flags and currency.

A currency symbol is declared, never guessed. With CURRENCY set and a symbol declared, the symbol is accepted once, leading (before or after the sign: $5, -$5, $ -5) or trailing (5 €, 1.234,50 kr.), with optional whitespace between it and the digits, and accounting parentheses wrap the symbol along with the digits (($5)). Declared but with the flag off, the symbol is simply the first offending byte of a MALFORMED fault; with no symbol declared the flag matches nothing. A symbol is 1 to 16 UTF-8 bytes with no ASCII digit or whitespace — anything else is a ValueError at construction, a caller bug like equal separators.

dollars = hypercast.NumFormat(".", ",", hypercast.NumFormat.ALL, "$")
hypercast.cast_i32("($1,234)", dollars)          # Success(value=-1234)
hypercast.cast_decimal("$1,234.50", dollars)     # Success(value=Decimal('1234.5'))

krone = hypercast.NumFormat(",", ".", hypercast.NumFormat.ALL, currency="kr.")
hypercast.cast_decimal("1.234,50 kr.", krone)    # Success(value=Decimal('1234.5'))

cast_decimal is the real doors' grammar with an exact result: a decimal.Decimal built from the core's sign, 96-bit magnitude and base-10 scale, never a float in between. The result is canonical: exact trailing zeros in the fraction are trimmed, so "0.1" is one tenth, "50%" is Decimal('0.5'), "1.10", "1.1" and "1.1000" are all Decimal('1.1') (as_tuple() gives digits (1, 1), exponent -1), and zero is Decimal('0'), never negative. Text past 96 bits of magnitude or 28 nonzero places is OUT_OF_RANGE — nothing but a zero is ever dropped, never rounded, the one thing a caller who reached for a decimal is entitled to assume.

hypercast.native_version() names the core actually loaded, "major.minor.patch", decoded from the same packed hypercast_version export every other binding probes. hypercast.BACKEND is always "native", the PyO3 extension.

In the browser (Pyodide)

The same PyO3 extension, compiled for Pyodide's Emscripten target, is published to PyPI as hypercast-X.Y.Z-cp311-abi3-pyemscripten_2026_0_wasm32.whl (about 150 KB), so micropip finds it the way pip finds the native wheels:

import micropip
await micropip.install("hypercast")

import hypercast
hypercast.cast_i32("(1,234)", hypercast.NumFormat.INVARIANT)   # Success(value=-1234)
hypercast.cast_timestamp("2026-01-02T10:04:05Z")

It is the native backend (hypercast.BACKEND == "native"), with the same API and no JavaScript bridge: every door is the same Rust call it is in CPython, and the verdicts are bit-for-bit the same. CI installs the wheel into Pyodide and runs this package's whole pytest suite in it twice, under Node and in headless Chrome, shared corpus replay included.

The wheel is for Pyodide 314.x (Python 3.14, platform pyemscripten_2026_0). It is abi3, but a Pyodide ABI is one Python minor built with one exact Emscripten, so each Pyodide ABI year needs its own wheel: earlier Pyodide lines (0.29.x and older) find no wheel, and the next line is covered by the release that adds its build.

Why not int() / fromisoformat / dateutil?

1. Verdicts, not exceptions — bad data is the expected case for untrusted text, and a Fault is a reason plus a span, not a ValueError to catch and regex.
2. The vocabulary untrusted sources actually send — twenty boolean lexemes, accounting parentheses, declared separators and currency symbols, radix prefixes, all five .NET Guid text forms plus urn:uuid: prefixes, protobuf JSON durations — with each lenience individually declared, never guessed.
3. One engine across a polyglot system — bit-for-bit verdicts with every other binding, held by the shared corpus (the whole suite green, in CPython and in Pyodide, the full corpus replayed).
4. Native-extension speed — the escape from the interpreted tier is this binding's own receipt: the old losses were never "Python calling native code," they were ctypes (~1 µs of interpreted marshalling per call, measured). The numbers are under Benchmarks.

The honest trade-off: for plain invariant integers int() still wins — it's a C-accelerated builtin with no boundary to cross. These doors earn their keep on the culture-machinery parsers, the closed error contract, and cross-language agreement.

Benchmarks

With the mechanism replaced, every door runs roughly an order of magnitude faster than it did over ctypes, where each cost about 3 µs. Measured with pyperf on linux-x64 (an Intel Core i9-11900H), CPython 3.14.7 as Fedora builds it, each door beside the closest thing the stdlib has:

The messy-feed doors are where the gap is widest, because strptime is the only stdlib parser that accepts their input at all — and it is slow. The three losses are each to a C builtin that reads one shape and has no boundary to cross: int() and float() on plain numbers, and fromisoformat on a timestamp. What a door returns for the difference is a verdict rather than an exception, and the forgiveness — grouping, declared separators, a currency symbol — at ~115-160 ns for grammar the stdlib doesn't sell at any price.

Past the parse, what a door costs is the Python object it hands back, so those are built the cheapest way the stable ABI allows: a uuid.UUID is allocated and its slots set through the C API with no __init__ (the core has already validated the text); a datetime, date or time comes from the packed form the datetime module's own pickling uses; and a timedelta from subtracting two datetimes, which is several times cheaper than its constructor. One abi3 wheel still covers every CPython from 3.11.

Separator detection costs ~15 ns: 1.234.567,89 under NumFormat.DETECT is 157 ns against 142 ns for the same text under a declared eurozone format.

Reproduce: maturin develop --release (from python/, inside a virtualenv — pyproject.toml already points maturin at ../rust/Cargo.toml and the python feature) to build the release extension, then pip install pyperf and python bench_cast.py --fast.

Verifying provenance

Every wheel PyPI serves, the Pyodide one included, carries a GitHub build-provenance attestation. The wheels are built, installed and attested in CI by the shared hyper-build-wheels.yml workflow in SkunkWerkx/.github, and release.yml verifies each one before publishing it unchanged, so the verify command names that signer:

pip download hypercast==X.Y.Z --no-deps -d .
gh attestation verify hypercast-X.Y.Z-*.whl \
  --repo SkunkWerkx/HyperCast --signer-repo SkunkWerkx/.github
# or: gh attestation verify hypercast-X.Y.Z-*.whl --owner SkunkWerkx

This is a separate thing from the PEP 740 attestations gh-action-pypi-publish already sends to PyPI itself, which PyPI-side tooling checks on its own — this is the GitHub/Sigstore transparency-log route, checked with gh attestation verify, the same route every other artifact in this project uses. See csharp/README.md's provenance section for why an artifact signed by the shared workflow needs --signer-repo.

License

MIT