cadrumo.core.calendar_shift module

Shift a date by whole calendar years, for legal periods counted de fecha a fecha.

Spanish tax provisions count several periods in whole years measured from a date: the LGT art. 66 prescription horizon, and the LIRPF art. 23.2.c rehabilitation window that admits a rehabilitation finalizada en los dos años anteriores a la fecha de la celebración del contrato. Both mean the same arithmetic and neither means a day count.

A year is not 365 days, and the difference is not academic. Two calendar years are 731 days whenever the span contains a 29 February, so a 730-day approximation falls one day short for roughly one date in four. The rehabilitation window shipped that way and denied the 60 per cent reducción to filers whose rehabilitation finished exactly two calendar years before the contract – a taxpayer detriment produced entirely by the unit, with every figure in the rule correct.

The leap day itself has no counterpart in a non-leap year, so a boundary landing on 29 February clamps to 28 February. That widens a backwards-looking window by one day rather than narrowing it, which is the direction that cannot cost a taxpayer a right they hold.

shift_by_calendar_years(moment, years)

Return moment shifted by whole calendar years, preserving its type.

Accepts a negative years to look backwards, which is how a lookback window expresses “the N years before this date” without any consumer subtracting days.

Parameters:

• moment (TypeVar(CalendarMoment, bound= date)) – The date or datetime to shift. The concrete type is preserved, so a datetime keeps its time and tzinfo.

• years (int) – Whole calendar years to add; negative shifts backwards.

Return type:

TypeVar(CalendarMoment, bound= date)

Returns:

The shifted moment, with a 29 February boundary clamped to 28 February when the target year is not a leap year.