fastfields-helpers

The shared, dependency-free Python layer of the fastfields stack: the Spline and Bound enums, and the argument-normalisation helpers that every wrapper (fastfields.numpy, fastfields.torch, fastfields.cupy) and the fastfields.auto dispatcher share.

fromfastfields.helpersimportSpline, Bound, as_spline, as_boundas_spline("cubic") # 3as_bound("wrap") # 6 == int(Bound.DFT)as_spline(Spline.Linear) # 1

Install

pip install fastfields-helpers

There is nothing to compile and nothing else to install: this package imports only the standard library.

Why it exists

These helpers used to live inside fastfields-dlpack, alongside the compiled nanobind extension. That meant a one-line fix to a string alias or a rounding rule could only reach users through a full compiled-wheel release cycle, built and published for every platform.

Splitting them out makes that cost disappear: fastfields-helpers is a plain universal wheel, so pure-Python fixes ship on their own. fastfields-helpers and fastfields-dlpack are independent siblings — neither depends on the other.

Public API

Enums:

• Spline — interpolation order, Nearest (0) through SeventhOrder (7).
• Bound — boundary condition: Zero, Replicate, DCT1, DCT2, DST1, DST2, DFT, NoCheck.

Normalisers — each accepts an int, an enum member, or a friendly string alias ("cubic", "dct2", "wrap", "neumann", …) and returns an int:

• as_spline(value)
• as_bound(value)

Shape / dimension resolution:

• normalize_shape(shape, ndim) — scalar-or-sequence → list[int] of length ndim.
• infer_ndim(ndim, factor, shape) — infer the number of trailing spatial dimensions.
• check_ndim(ndim, arr_ndim) — validate 1 <= ndim <= arr_ndim.
• resolve_out_spatial(spatial_in, ndim, factor, shape) — output spatial shape from a factor or an explicit shape (mutually exclusive; neither means identity).

torch-interpol anchor conventions:

• anchor_scale_shift(anchor, inshape, outshape, ndim) — map a centers/edges/first/last anchor (or its first-letter abbreviation) onto the per-dim scale and scalar shift the resize binding consumes.

See the API reference for full signatures.