Are you tired of plain old integer-based indexing? Use floats instead!

float-indexing.py

"""
Are you tired of plain old integer-based indexing?

Use floats instead!
"""

# Author: Markus H (MawKKe) 2024-04 https://github.com/MawKKe

import math
import typing as t

import pytest

def lerp(a, b, scale: float) -> float:
    assert 0 <= scale <= 1
    return (b-a) * scale + a

class InterpList(list):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.interp = kwargs.pop('interp', lerp)

    def __getitem__(self, i: t.Union[float, int]):
        a = super().__getitem__(math.floor(i))
        b = super().__getitem__(math.ceil(i))
        scale = i - math.floor(i)
        return self.interp(a, b, scale)

def test_interplist():
    l = InterpList([2, 7, -1, 8])

    # old school integer indexing. ugh, so boring...
    assert l[0] == 2
    assert l[1] == 7
    assert l[2] == -1
    assert l[3] == 8

    # index with floats, as mother nature intended
    assert l[0.5]   == pytest.approx(4.5,     0.001)
    assert l[1.98]  == pytest.approx(-0.8399, 0.001)
    assert l[2.458] == pytest.approx(3.12,    0.001)

def test_interplist_fract():
    from fractions import Fraction as F

    l = InterpList([F(2,7), F(1,8), -F(2,81)])

    assert l[F(1,2)] == F(23, 112)
    assert l[1 + F(98,100)] == F(-703, 32400)