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- 「²」这类字符 isdigit 为真、int() 却认不得：写进 cron 或每页条数时会冒出英文的 ValueError（被全局处理器 回成 400）。改按 isdecimal 认，照常回中文的 422 - 库里的 cron 或时区后来坏了时，立即运行记下的原因以前写「输入模板无法渲染」，其实模板没错：改成照实说 「无法生成这次运行的输入」，后面跟是哪一项
378 lines
17 KiB
Python
378 lines
17 KiB
Python
"""五字段 cron：解析、下次 / 上次触发、中文描述。
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自己写而不加依赖：要的只是五个字段（分 时 日 月 周）的标准写法，再加两条现成的库各有各的做法、说不清楚
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的规则——夏令时，和日、周都写了的时候取「或」还是「且」。
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- 每个字段可写 *、列表（1,15）、范围（1-5）、步长（*/15、10-50/20、5/20），月和周可写英文缩写（JAN、MON），
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不分大小写；周日写 0 或 7。L、W、#、?、@daily 这些扩展写法不支持，报错说明
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- 日和周：两个都受限（都不以 * 开头）时，满足任一个就触发；有一个以 * 开头，就只看另一个。以 * 开头的步长
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（*/2）也算没受限——和 Linux 系统的 cron（Vixie / cronie）一致，同一个表达式在这里和在服务器上意思相同
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- 时间按任务时区的墙上时间匹配：夏令时拨快时跳过的本地时间（纽约 3 月的 02:30）那天不触发，不顺延；拨回时
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重复出现的本地时间（纽约 11 月的 01:30）只在第一次出现时触发一次
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"""
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from __future__ import annotations
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from dataclasses import dataclass
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from datetime import date, datetime, timedelta, timezone
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from functools import lru_cache
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from zoneinfo import ZoneInfo, available_timezones
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UTC = timezone.utc
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#: 字段的键、界面上的叫法、取值范围
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_FIELDS = (
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("minute", "分", 0, 59),
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("hour", "时", 0, 23),
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("day", "日", 1, 31),
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("month", "月", 1, 12),
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("weekday", "周", 0, 7),
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)
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_ALLOWED = {
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"minute": "0–59",
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"hour": "0–23",
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"day": "1–31",
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"month": "1–12 或 JAN–DEC",
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"weekday": "0–7（0 和 7 都是周日）或 SUN–SAT",
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}
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_MONTH_NAMES = {name: i + 1 for i, name in enumerate(
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("JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC"))}
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_WEEKDAY_NAMES = {name: i for i, name in enumerate(("SUN", "MON", "TUE", "WED", "THU", "FRI", "SAT"))}
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#: 每个月最多有几天：2 月按闰年算（2 月 29 日四年一次，不算永远不会触发）
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_MONTH_DAYS = {1: 31, 2: 29, 3: 31, 4: 30, 5: 31, 6: 30, 7: 31, 8: 31, 9: 30, 10: 31, 11: 30, 12: 31}
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#: 往后（往前）找触发时间最多找几年。2 月 29 日最长要等 8 年（2096 年之后是 2104 年）
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_HORIZON_YEARS = 9
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#: 夏令时一次最多拨动多少（历史上有过拨 2 小时的），往前找时据此跳过不可能的墙上时间
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_MAX_SHIFT = timedelta(hours=3)
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_WEEKDAY_LABEL = {0: "周日", 1: "周一", 2: "周二", 3: "周三", 4: "周四", 5: "周五", 6: "周六"}
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class CronError(ValueError):
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"""表达式写错了。str() 是给人看的中文说明；field 是出错的字段（minute / hour / day / month / weekday），
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说的是整个表达式（字段个数不对、永远不会触发）时为 None。"""
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def __init__(self, message: str, field: str | None = None) -> None:
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super().__init__(message)
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self.field = field
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class TimezoneError(ValueError):
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"""时区名认不出。str() 是给人看的中文说明。"""
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@dataclass(frozen=True)
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class CronSpec:
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"""解析好的表达式。expr 是规范化后的原文（字段之间一个空格），描述、报错里引用它。"""
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expr: str
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minutes: tuple[int, ...]
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hours: tuple[int, ...]
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days: frozenset[int]
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months: frozenset[int]
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#: 0 是周日，6 是周六（写 7 的已经换成 0）
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weekdays: frozenset[int]
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#: 日、周字段是不是以 * 开头（没受限）。两个都受限时取「或」
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day_star: bool
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weekday_star: bool
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def matches_day(self, day: date) -> bool:
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if day.month not in self.months:
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return False
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in_days = day.day in self.days
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# date.weekday() 周一是 0；cron 周日是 0
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in_weekdays = (day.weekday() + 1) % 7 in self.weekdays
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if self.day_star or self.weekday_star:
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return in_days and in_weekdays
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return in_days or in_weekdays
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# --------------------------------------------------------------------------
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# 解析
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# --------------------------------------------------------------------------
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def parse(expr: str | CronSpec) -> CronSpec:
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"""解析五字段表达式。写错抛 CronError（中文说明，指出字段和允许的范围）。"""
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if isinstance(expr, CronSpec):
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return expr
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parts = str(expr or "").split()
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if not parts:
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raise CronError("cron 表达式不能为空，需要 5 个字段（分 时 日 月 周），例如 0 9 * * 1 表示每周一 09:00")
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if len(parts) != 5:
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raise CronError(f"cron 表达式需要 5 个字段（分 时 日 月 周），用空格分隔；现在有 {len(parts)} 个")
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values = [_parse_field(text, *meta) for text, meta in zip(parts, _FIELDS)]
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spec = CronSpec(
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expr=" ".join(parts),
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minutes=tuple(sorted(values[0])),
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hours=tuple(sorted(values[1])),
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days=frozenset(values[2]),
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months=frozenset(values[3]),
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weekdays=frozenset(v % 7 for v in values[4]),
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day_star=parts[2].startswith("*"),
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weekday_star=parts[4].startswith("*"),
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)
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_refuse_never(spec)
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return spec
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def _parse_field(text: str, key: str, label: str, low: int, high: int) -> set[int]:
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out: set[int] = set()
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for item in text.split(","):
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if not item:
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raise CronError(f"「{label}」字段「{text}」里有空的列表项，允许 {_ALLOWED[key]}", key)
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out |= _parse_item(item, key, label, low, high)
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return out
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def _parse_item(item: str, key: str, label: str, low: int, high: int) -> set[int]:
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base, slash, step_text = item.partition("/")
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step = 1
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if slash:
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# isdecimal 而不是 isdigit：「²」算 digit，int() 却认不得它
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if not step_text.isdecimal() or int(step_text) == 0:
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raise CronError(f"「{label}」字段「{item}」的步长需要是正整数，现在是「{step_text}」", key)
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step = int(step_text)
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if base == "*":
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start, end = low, high
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elif "-" in base:
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left, _, right = base.partition("-")
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start = _value(left, item, key, label, low, high)
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end = _value(right, item, key, label, low, high, range_end=True)
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if start > end:
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raise CronError(f"「{label}」字段的范围「{base}」起点大于终点", key)
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else:
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start = _value(base, item, key, label, low, high)
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# 「5/20」是从 5 到最大值、每 20 一个；不带步长就是这一个值
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end = high if slash else start
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if key == "weekday" and base == "*":
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end = 6 # * 是周日到周六，7 和 0 是同一天
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return set(range(start, end + 1, step))
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def _value(token: str, item: str, key: str, label: str, low: int, high: int, *, range_end: bool = False) -> int:
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word = token.strip().upper()
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if word.isdecimal():
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number = int(word)
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if not low <= number <= high:
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raise CronError(f"「{label}」字段的 {number} 超出范围，允许 {_ALLOWED[key]}", key)
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return number
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names = _MONTH_NAMES if key == "month" else _WEEKDAY_NAMES if key == "weekday" else None
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if word.isalpha() and names is None:
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raise CronError(f"「{label}」字段不能使用英文缩写「{token}」，只有「月」和「周」字段可以，允许 {_ALLOWED[key]}", key)
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if names is not None and word in names:
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number = names[word]
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# MON-SUN 是周一到周日：范围终点的 SUN 当 7
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return 7 if key == "weekday" and range_end and number == 0 else number
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raise CronError(
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f"「{label}」字段无法识别「{item}」，允许 {_ALLOWED[key]}，可以写 *、列表（1,15）、范围（1-5）和步长（*/10）", key)
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def _refuse_never(spec: CronSpec) -> None:
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"""日受限、周没受限时，所写的日子在所写的月份里一天都不存在（2 月 30 日、小月的 31 日）就永远不会触发。
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周受限时总有符合的那一天，不用查。"""
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if spec.day_star or not spec.weekday_star:
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return
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if any(day <= _MONTH_DAYS[month] for month in spec.months for day in spec.days):
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return
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raise CronError("这个 cron 表达式永远不会触发：所写的日期在所写的月份里不存在（例如 2 月没有 30 日）", "day")
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# --------------------------------------------------------------------------
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# 时区
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# --------------------------------------------------------------------------
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@lru_cache(maxsize=1)
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def _zones() -> dict[str, str]:
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"""小写名 → 规范名。在不区分大小写的文件系统上 ZoneInfo("asia/shanghai") 也能打开，存进去的却不是规范名，
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换到 Linux 上就打不开了：一律对照时区库的清单换成规范名。"""
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return {name.lower(): name for name in available_timezones()}
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def timezone_name(name: str) -> str:
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"""规范的 IANA 时区名。认不出抛 TimezoneError。"""
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text = str(name or "").strip()
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canonical = _zones().get(text.lower()) if text else None
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if canonical is None:
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shown = f"「{text}」" if text else "（未填写）"
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raise TimezoneError(f"无法识别的时区{shown}，请填写 IANA 时区名，例如 Asia/Shanghai")
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return canonical
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def zone(name: str | ZoneInfo) -> ZoneInfo:
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if isinstance(name, ZoneInfo):
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return name
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return ZoneInfo(timezone_name(name))
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# --------------------------------------------------------------------------
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# 触发时间
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# --------------------------------------------------------------------------
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def _instant(local: datetime, tz: ZoneInfo) -> datetime | None:
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"""本地墙上时间 → UTC 时刻。拨快时跳过的本地时间不存在，返回 None；拨回时重复的取第一次出现（fold=0）。
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zoneinfo 对不存在的本地时间按拨快前的偏移换算，换回本地就对不上原来的墙上时间——据此认出它。按 fold=0
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换算，本地时间越晚时刻也越晚，往后找到的第一个就是最早的那个。"""
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aware = local.replace(tzinfo=tz, fold=0)
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moment = aware.astimezone(UTC)
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if moment.astimezone(tz).replace(tzinfo=None) != local:
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return None
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return moment
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def _days(start: date, step: int, spec: CronSpec):
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"""从 start 起逐日往后（step=1）或往前（step=-1）走，只交出符合月、日、周的那些天。不在所写月份里的整月跳过。"""
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day = start
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limit = timedelta(days=366 * _HORIZON_YEARS)
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stop = start + limit if step > 0 else start - limit
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while (day <= stop) if step > 0 else (day >= stop):
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if day.month not in spec.months:
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if step > 0:
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day = (day.replace(day=1) + timedelta(days=32)).replace(day=1)
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else:
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day = day.replace(day=1) - timedelta(days=1)
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continue
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if spec.matches_day(day):
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yield day
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day += timedelta(days=step)
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def next_fire(expr: str | CronSpec, tz: str | ZoneInfo, after: datetime) -> datetime | None:
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"""after 之后（不含）最早的一次触发，UTC。找不到（只在夏令时把仅有的那几个时刻全跳过时）返回 None。"""
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spec, zone_info = parse(expr), zone(tz)
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after = _aware(after)
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local = after.astimezone(zone_info).replace(tzinfo=None)
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floor = local.replace(second=0, microsecond=0)
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for day in _days(local.date(), 1, spec):
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for hour in spec.hours:
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for minute in spec.minutes:
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candidate = datetime(day.year, day.month, day.day, hour, minute)
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# 墙上时间早于 after 的那一分钟，时刻必定也早于 after（拨回那天第二遍的 after 更是如此），不用换算
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if candidate < floor:
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continue
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moment = _instant(candidate, zone_info)
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if moment is not None and moment > after:
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return moment
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return None
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def prev_fire(expr: str | CronSpec, tz: str | ZoneInfo, before: datetime) -> datetime | None:
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"""before 之前（不含）最近的一次触发，UTC。拨回那天第二遍的时刻往前找，第一遍出现的同一本地时间算已经触发过。"""
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spec, zone_info = parse(expr), zone(tz)
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before = _aware(before)
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local = before.astimezone(zone_info).replace(tzinfo=None)
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for day in _days(local.date(), -1, spec):
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for hour in reversed(spec.hours):
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for minute in reversed(spec.minutes):
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candidate = datetime(day.year, day.month, day.day, hour, minute)
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# 只按时刻比较：第二遍的 01:40 之前，墙上时间更晚的第一遍 01:50 也算。超出夏令时最大拨动幅度的不可能
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if candidate > local + _MAX_SHIFT:
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continue
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moment = _instant(candidate, zone_info)
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if moment is not None and moment < before:
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return moment
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return None
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def last_due(expr: str | CronSpec, tz: str | ZoneInfo, at: datetime) -> datetime | None:
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"""at 之前（含）最近的一次触发，UTC。"""
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return prev_fire(expr, tz, _aware(at) + timedelta(microseconds=1))
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def preview(expr: str | CronSpec, tz: str | ZoneInfo, n: int = 5, *, after: datetime | None = None) -> list[datetime]:
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"""after（默认现在）之后的 n 次触发，UTC。"""
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spec, zone_info = parse(expr), zone(tz)
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out: list[datetime] = []
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cursor = _aware(after) if after is not None else datetime.now(UTC)
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while len(out) < n:
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moment = next_fire(spec, zone_info, cursor)
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if moment is None:
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break
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out.append(moment)
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cursor = moment
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return out
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def _aware(value: datetime) -> datetime:
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"""不带时区的按 UTC 算（库里读出来的都带，这里只防调用方传 naive 的）。"""
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return value if value.tzinfo is not None else value.replace(tzinfo=UTC)
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# --------------------------------------------------------------------------
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# 中文描述
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# --------------------------------------------------------------------------
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def describe(expr: str | CronSpec, tz: str) -> str:
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"""「每周一 09:00（Asia/Shanghai）」。说不清的写「按 cron 表达式 x（时区）」。"""
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spec = parse(expr)
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return f"{_describe(spec) or f'按 cron 表达式 {spec.expr}'}（{tz}）"
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def _describe(spec: CronSpec) -> str | None:
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all_days = spec.days == frozenset(range(1, 32))
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all_weekdays = spec.weekdays == frozenset(range(7))
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all_months = spec.months == frozenset(range(1, 13))
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# 日、周都受限时取「或」：有一边是全部，那就是每天；两边都只写了一部分就说不清，交给兜底
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either = not (spec.day_star or spec.weekday_star)
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every_day = (all_days and all_weekdays) or (either and (all_days or all_weekdays))
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# 日写的 *（以 * 开头、且确实是全部日子）时只看周；周写的 * 时只看日。*/2 这种以 * 开头的步长不是全部
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weekly = not every_day and spec.day_star and all_days
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monthly = not every_day and spec.weekday_star and all_weekdays
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if every_day and all_months:
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if spec.minutes == tuple(range(60)) and spec.hours == tuple(range(24)):
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return "每分钟"
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step = _step_of(spec.minutes, 60)
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if step and spec.hours == tuple(range(24)):
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return f"每 {step} 分钟"
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if len(spec.minutes) != 1:
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return None
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minute = spec.minutes[0]
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if every_day and all_months:
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if spec.hours == tuple(range(24)):
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return "每小时整点" if minute == 0 else f"每小时第 {minute} 分钟"
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step = _step_of(spec.hours, 24)
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if step:
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return f"每 {step} 小时" if minute == 0 else f"每 {step} 小时（第 {minute} 分钟）"
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if len(spec.hours) > 4:
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return None
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times = "、".join(f"{hour:02d}:{minute:02d}" for hour in spec.hours)
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if every_day and all_months:
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return f"每天 {times}"
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if weekly and all_months:
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return f"每{_weekdays_text(spec.weekdays)} {times}"
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if not monthly or len(spec.days) > 4:
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return None
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days = "、".join(f"{day} 日" for day in sorted(spec.days))
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if all_months:
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return f"每月 {days} {times}"
|
||
if len(spec.months) == 1:
|
||
month = next(iter(spec.months))
|
||
if month == 2 and spec.days == frozenset({29}):
|
||
return f"每逢闰年 2 月 29 日 {times}"
|
||
return f"每年 {month} 月 {days} {times}"
|
||
return None
|
||
|
||
|
||
def _step_of(values: tuple[int, ...], size: int) -> int | None:
|
||
"""values 是不是从 0 起、每 n 一个、整除 size 的等差（*/n）：是就返回 n（大于 1）。不整除的（*/7 分钟）到了
|
||
整点会重新数，说成「每 7 分钟」就不对了。"""
|
||
if len(values) < 2 or values[0] != 0:
|
||
return None
|
||
step = values[1] - values[0]
|
||
if step <= 1 or size % step or values != tuple(range(0, size, step)):
|
||
return None
|
||
return step
|
||
|
||
|
||
def _weekdays_text(weekdays: frozenset[int]) -> str:
|
||
"""周一在前、周日在后。连续三天以上写「周一至周五」。"""
|
||
ordered = sorted(weekdays, key=lambda d: (d - 1) % 7)
|
||
positions = [(d - 1) % 7 for d in ordered]
|
||
if len(ordered) >= 3 and positions == list(range(positions[0], positions[0] + len(positions))):
|
||
return f"{_WEEKDAY_LABEL[ordered[0]]}至{_WEEKDAY_LABEL[ordered[-1]]}"
|
||
return "、".join(_WEEKDAY_LABEL[d] for d in ordered)
|
||
|