Format timestamp safe for filename

filenameSafeTimestamp.mjs

const TZLETTER = new Map([
	[0, "Z"],
	[60, "N"],
	[120, "O"],
	[180, "P"],
	[210, "P30"],
	[240, "Q"],
	[300, "R"],
	[360, "S"],
	[420, "T"],
	[480, "U"],
	[540, "V"],
	[570, "V30"],
	[600, "W"],
	[660, "X"],
	[720, "Y"],
	[-840, "MB"],
	[-780, "MA"],
	[-765, "M45"],
	[-720, "M"],
	[-660, "L"],
	[-630, "K30"],
	[-600, "K"],
	[-570, "I30"],
	[-540, "I"],
	[-525, "H45"],
	[-480, "H"],
	[-420, "G"],
	[-390, "F30"],
	[-360, "F"],
	[-330, "E30"],
	[-300, "E"],
	[-270, "D30"],
	[-240, "D"],
	[-210, "C30"],
	[-180, "C"],
	[-120, "B"],
	[-60, "A"],
]);

TZLETTER.default = "J";


export default function filenameSafeTimestamp(d, useLocalTime=true) {
	if (d === undefined)
		d = new Date();

	return (
		useLocalTime
		? `${d.getFullYear().toString().padStart(4, "0")}-${(d.getMonth()+1).toString().padStart(2, "0")}-${d.getDate().toString().padStart(2, "0")}T${d.getHours().toString().padStart(2, "0")}-${d.getMinutes().toString().padStart(2, "0")}-${d.getSeconds().toString().padStart(2, "0")}${TZLETTER.get(d.getTimezoneOffset()) ?? TZLETTER.default}`
		: `${d.getUTCFullYear().toString().padStart(4, "0")}-${(d.getUTCMonth()+1).toString().padStart(2, "0")}-${d.getUTCDate().toString().padStart(2, "0")}T${d.getUTCHours().toString().padStart(2, "0")}-${d.getUTCMinutes().toString().padStart(2, "0")}-${d.getUTCSeconds().toString().padStart(2, "0")}${TZLETTER.get(0)}`
	);
}

filenameSafeTimestamp.py

import datetime
import sys

__all__ = ['datetime_format_filename']


TZLETTER = {
    datetime.timedelta(hours=0): "Z",
    datetime.timedelta(hours=-1): "N",
    datetime.timedelta(hours=-2): "O",
    datetime.timedelta(hours=-3): "P",
    datetime.timedelta(hours=-4.5): "P30",
    datetime.timedelta(hours=-4): "Q",
    datetime.timedelta(hours=-5): "R",
    datetime.timedelta(hours=-6): "S",
    datetime.timedelta(hours=-7): "T",
    datetime.timedelta(hours=-8): "U",
    datetime.timedelta(hours=-9): "V",
    datetime.timedelta(hours=-10.5): "V30",
    datetime.timedelta(hours=-10): "W",
    datetime.timedelta(hours=-11): "X",
    datetime.timedelta(hours=-12): "Y",
    datetime.timedelta(hours=14): "MB",
    datetime.timedelta(hours=13): "MA",
    datetime.timedelta(hours=12.75): "M45",
    datetime.timedelta(hours=12): "M",
    datetime.timedelta(hours=11): "L",
    datetime.timedelta(hours=10.5): "K30",
    datetime.timedelta(hours=10): "K",
    datetime.timedelta(hours=9.5): "I30",
    datetime.timedelta(hours=9): "I",
    datetime.timedelta(hours=8.75): "H45",
    datetime.timedelta(hours=8): "H",
    datetime.timedelta(hours=7): "G",
    datetime.timedelta(hours=6.5): "F30",
    datetime.timedelta(hours=6): "F",
    datetime.timedelta(hours=5.5): "E30",
    datetime.timedelta(hours=5): "E",
    datetime.timedelta(hours=4.5): "D30",
    datetime.timedelta(hours=4): "D",
    datetime.timedelta(hours=3.5): "C30",
    datetime.timedelta(hours=3): "C",
    datetime.timedelta(hours=2): "B",
    datetime.timedelta(hours=1): "A",
    None: "J"
}


if sys.version_info >= (3, 12):
    UTC = datetime.UTC
    _UTC_REPR = "datetime.UTC"

    def _naivelocalnow():
        return datetime.now()

    def localnow():
        return _naivelocalnow().astimezone()

    def utcnow_():
        return datetime.now(tz=utc)
else:
    UTC = datetime.timezone.utc
    _UTC_REPR = "datetime.timezone.utc"

    def _naivelocalnow():
        return datetime.datetime.now()

    def localnow():
        return _naivelocalnow().astimezone()

    def utcnow_():
        return datetime.datetime.now(tz=UTC)


def datetime_format_filename(dt=None, *, _format="%Y-%m-%dT%H-%M-%S%!Z", local=True):
    if dt is None:
        dt = localnow() if local else utcnow_()

    utcoffset = dt.utcoffset()

    if utcoffset is None:
        if not local:
            raise TypeError(f"datetime_format_filename(..., local=False) called on a naive datetime object. If you meant it to be interpreted as being in the system timezone, call .astimezone() on it first; if you meant it to be interpreted as UTC, call .replace(tzinfo={_UTC_REPR}) on it first.")
    
    if not local:
        dt = dt.astimezone(UTC)

    return dt.strftime(_format.replace("%!Z", TZLETTER.get(utcoffset, TZLETTER[None])))