reference calendar

Business Day Calendar Reference

lclang.utils.calendar is an async-first, three-state calendar algebra. A calendar maps every datetime.date to DayType.BusinessDay, DayType.Holiday, or DayType.Undefined. Undefined means that the calendar has no opinion; it is not another spelling for holiday.

Identity, dates, and failures

Every BDCalendar has one immutable CalendarID. Equality, hashing, manager caches, dependency sets, and canonical compositions use that ID. Configuration collections are detached and read-only. Classification and mapping caches are mutable implementation snapshots exposed through read-only views.

get_day_type(d) classifies a date. next_bd(d) and prev_bd(d) are strict; this_or_next_bd(d) and this_or_prev_bd(d) retain d when it is already a business day. Functional and year-batch traversal searches at most MAX_BUSINESS_DAY_GAP_DAYS (1,000) days. gen_year(year) accepts years 1 through 9999 and may omit undefined dates.

• DateOperationOutOfScopeException retains source_date and source_calendar.
• CalendarCannotLoadException retains the requested calendar_id.
• CalendarLogicException retains the failing calendar_id and chains the original traceback.
• UnappliedCalendarOperationException reports a mapping without a source.

These are ordinary Python exceptions. Through LCL, the evaluator wraps them in its normal source-aware LclEvaluationError.

Storage strategies

HardcodedBDCalendar stores an immutable explicit mapping; missing dates are undefined. FunctionalBDCalendar supplies bounded traversal around an abstract per-date classifier. ForwardStepBDCalendar discovers a sparse increasing business-date sequence from first_bd. YearBatchBDCalendar loads and caches one validated mapping per year. Custom subclasses implement the public abstract method named by their strategy and honor the cache and failure contract.

Calendar algebra

Method	Operator	Meaning
union	+	Business wins, then holiday, then undefined.
intersect	&	All-undefined stays undefined; any holiday vetoes.
minus	-	Matching subtrahend business days become holidays.
fallback	>>	Return the first non-undefined value in order.
revert	~	Exchange business and holiday; retain undefined.

Union, intersection, and subtraction operands are sorted and deduplicated by calendar ID. Fallback order is significant. business_days() removes holiday classifications; holidays() removes business classifications. Repeated filters are idempotent, and double reversal returns the original calendar.

Builtins and factories

Total singletons are ALL_DAYS, ALL_WEEKDAYS, MONDAYS through SUNDAYS, BEGIN_OF_MONTHS, END_OF_MONTHS, BEGIN_OF_YEARS, and END_OF_YEARS. Nonmatching dates are holidays. BUILTIN_CALENDARS maps every singleton ID to that exact object.

at(*dates) accepts date, strict YYYYMMDD strings, or padded integers. nth_day_of_month(*n) and nth_business_day_of_month(calendar, *n) accept -31..-1 and 1..31; negative values count backward. range_start_days and range_end_days select boundaries of contiguous business ranges. def_functional_calendar accepts sync or async classifier and dependency callables and validates their results.

Date mappings

map_this_or_next(calendar=None), map_this_or_prev(calendar=None), and shift_n_days(n, calendar=None) create immutable BDCalendarMapping chains. Omitting the operation calendar binds it to the source. A standalone chain may use SELF_CALENDAR until await mapping.apply(calendar) supplies the source.

Each primitive moves at most MAX_BUSINESS_DAY_SHIFT_DAYS (100) calendar days; a chain may accumulate more. Zero shift has this-or-next semantics. Positive and negative values use strict next and previous dates. map_date_reverse returns the inclusive monotonic source range mapped to a target.

await mapping.as_calendar() creates a CalendarMapBDCalendar. A target is business only when at least one source business date maps to it.

Named loading and retirement

BuiltinBDCalendarLoader returns singleton builtins. FileSystemHardcodedBDCalendarLoader looks for <calendar-id>.calendar.json beneath its configured directory:

{
  "business_days": ["20240102", "20240103"],
  "holidays": ["20240101"]
}

The UTF-8 JSON object has exactly those arrays. Dates are unique strict strings and cannot overlap. Malformed, unsafe, or non-file matches raise CalendarCannotLoadException; absence lets the next loader try.

BDCalendarManager.use_calendar shares one in-flight load per ID and event loop, shields waiter cancellation, caches only success, detects dependency cycles, and validates returned IDs. Calendar fallbacks are uncached; ID fallbacks recurse. retire_calendar removes a cached calendar and recursive dependants, optionally installing a replacement.

use_calendar_manager(loaders) appends a builtin loader last when needed. use_file_system_hardcoded_calendar_loader(path) accepts Path or text.

LCL exposure

Canonical Frames expose the manager helpers and a read-only calendars namespace from LCL_BUILTINS. It contains DayType, all factories, and every singleton. Use calendars.DayType.BusinessDay. Standard iter, text, data, and json namespaces also live in LCL_BUILTINS; LCL_ROOT contains only definition-scoped lhs().

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