1c59f331f4
Option A (text-faithful): RateProblem gains time_unit (the duration's ORIGINAL unit; time stays int; defaults to the rate denominator). The SOLVER converts via convert_time -> exact Fraction -> int-or-refuse(non_integer); Fraction never leaves the solver, no floats. The reader accepts a convertible (minute<->hour) duration mismatch (keeps original time_unit); a non-convertible one still refuses rate_unit_mismatch. Signature includes time_unit ('30 minutes' != '30 hours').
Gold: r3-09 flips reader_refuses -> SOLVED (60 mph for 30 min = 30 mile, exact 1/2 hour; distractor 1800 rejected); new r3-13 non-convertible (3 gallons) stays rate_unit_mismatch. R3 gold 13/13; reader 9/0/0 -> answers 7/0/6 (setup_correct 8->9). Failure-family: rate_unit_mismatch now non-convertible-only -> still unsupported_rate_duration proposal surface; router-hygiene invariant stays green; R1 7/0/3, R2 10/0/0 unchanged. 119-test smoke green incl. invariants. Off-serving, no float path.
52 lines
2.1 KiB
Python
52 lines
2.1 KiB
Python
"""Exact rational time-unit conversion for R3.2 (single-rate only).
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The single new capability of R3.2: a duration whose unit differs from the rate's denominator may be
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**converted** when both are known time units (``minute`` ↔ ``hour``), instead of refusing. The
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conversion is **exact rational** (``fractions.Fraction``) — never a float, never a decimal:
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```text
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30 minutes -> Fraction(1, 2) hour
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90 minutes -> Fraction(3, 2) hour
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2 hours -> Fraction(120) minute
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```
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So ``60 mile/hour × 30 minute`` becomes ``60 × 1/2 = 30 mile`` (exact). A non-time / non-convertible
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pair (``minute`` ↔ ``mile``) raises ``ConversionError`` and the caller still refuses
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``rate_unit_mismatch`` — convertibility is the only thing R3.2 adds.
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Deliberately tiny: ONLY ``minute`` ↔ ``hour`` in v1. No length (mile↔km), no currency
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(dollar↔cent), no compound conversions, no clock-time intervals. Deterministic.
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"""
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from __future__ import annotations
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from fractions import Fraction
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class ConversionError(ValueError):
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"""The units are not a known convertible pair — the caller must refuse."""
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#: Each known time unit as an exact rational number of the base unit (one hour).
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_TIME_IN_HOURS: dict[str, Fraction] = {
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"hour": Fraction(1),
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"minute": Fraction(1, 60),
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}
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def is_convertible(from_unit: str, to_unit: str) -> bool:
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"""Whether a conversion exists — the identity (same unit, any kind) or a known time-unit pair."""
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return from_unit == to_unit or (from_unit in _TIME_IN_HOURS and to_unit in _TIME_IN_HOURS)
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def convert_time(value: int, from_unit: str, to_unit: str) -> Fraction:
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"""Exact rational conversion of *value* ``from_unit`` into *to_unit*. Identity for the same unit
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(any kind, e.g. ``box``); a known time-unit pair otherwise; refuses anything else."""
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if from_unit == to_unit:
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return Fraction(value)
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if from_unit not in _TIME_IN_HOURS or to_unit not in _TIME_IN_HOURS:
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raise ConversionError(f"no exact conversion {from_unit!r} -> {to_unit!r}")
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return Fraction(value) * _TIME_IN_HOURS[from_unit] / _TIME_IN_HOURS[to_unit]
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__all__ = ["ConversionError", "convert_time", "is_convertible"]
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