Source code for airflow.timetables._cron
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from __future__ import annotations
import datetime
from functools import cached_property
from typing import Any
from cron_descriptor import CasingTypeEnum, ExpressionDescriptor, FormatException, MissingFieldException
from croniter import CroniterBadCronError, CroniterBadDateError, croniter
from pendulum import DateTime
from pendulum.tz.timezone import Timezone
from airflow.exceptions import AirflowTimetableInvalid
from airflow.utils.dates import cron_presets
from airflow.utils.timezone import convert_to_utc, make_aware, make_naive
def _is_schedule_fixed(expression: str) -> bool:
"""Figures out if the schedule has a fixed time (e.g. 3 AM every day).
:return: True if the schedule has a fixed time, False if not.
Detection is done by "peeking" the next two cron trigger time; if the
two times have the same minute and hour value, the schedule is fixed,
and we *don't* need to perform the DST fix.
This assumes DST happens on whole minute changes (e.g. 12:59 -> 12:00).
"""
cron = croniter(expression)
next_a = cron.get_next(datetime.datetime)
next_b = cron.get_next(datetime.datetime)
return next_b.minute == next_a.minute and next_b.hour == next_a.hour
[docs]class CronMixin:
"""Mixin to provide interface to work with croniter."""
def __init__(self, cron: str, timezone: str | Timezone) -> None:
self._expression = cron_presets.get(cron, cron)
if isinstance(timezone, str):
timezone = Timezone(timezone)
self._timezone = timezone
descriptor = ExpressionDescriptor(
expression=self._expression, casing_type=CasingTypeEnum.Sentence, use_24hour_time_format=True
)
try:
# checking for more than 5 parameters in Cron and avoiding evaluation for now,
# as Croniter has inconsistent evaluation with other libraries
if len(croniter(self._expression).expanded) > 5:
raise FormatException()
interval_description: str = descriptor.get_description()
except (CroniterBadCronError, FormatException, MissingFieldException):
interval_description = ""
self.description: str = interval_description
[docs] def __eq__(self, other: Any) -> bool:
"""Both expression and timezone should match.
This is only for testing purposes and should not be relied on otherwise.
"""
if not isinstance(other, type(self)):
return NotImplemented
return self._expression == other._expression and self._timezone == other._timezone
@property
[docs] def summary(self) -> str:
return self._expression
[docs] def validate(self) -> None:
try:
croniter(self._expression)
except (CroniterBadCronError, CroniterBadDateError) as e:
raise AirflowTimetableInvalid(str(e))
@cached_property
def _should_fix_dst(self) -> bool:
# This is lazy so instantiating a schedule does not immediately raise
# an exception. Validity is checked with validate() during DAG-bagging.
return not _is_schedule_fixed(self._expression)
def _get_next(self, current: DateTime) -> DateTime:
"""Get the first schedule after specified time, with DST fixed."""
naive = make_naive(current, self._timezone)
cron = croniter(self._expression, start_time=naive)
scheduled = cron.get_next(datetime.datetime)
if not self._should_fix_dst:
return convert_to_utc(make_aware(scheduled, self._timezone))
delta = scheduled - naive
return convert_to_utc(current.in_timezone(self._timezone) + delta)
def _get_prev(self, current: DateTime) -> DateTime:
"""Get the first schedule before specified time, with DST fixed."""
naive = make_naive(current, self._timezone)
cron = croniter(self._expression, start_time=naive)
scheduled = cron.get_prev(datetime.datetime)
if not self._should_fix_dst:
return convert_to_utc(make_aware(scheduled, self._timezone))
delta = naive - scheduled
return convert_to_utc(current.in_timezone(self._timezone) - delta)
def _align_to_next(self, current: DateTime) -> DateTime:
"""Get the next scheduled time.
This is ``current + interval``, unless ``current`` falls right on the
interval boundary, when ``current`` is returned.
"""
next_time = self._get_next(current)
if self._get_prev(next_time) != current:
return next_time
return current
def _align_to_prev(self, current: DateTime) -> DateTime:
"""Get the prev scheduled time.
This is ``current - interval``, unless ``current`` falls right on the
interval boundary, when ``current`` is returned.
"""
prev_time = self._get_prev(current)
if self._get_next(prev_time) != current:
return prev_time
return current
