datetime and number

vue-i18n's d() and n(). Both need the intl extra:

pip install "vue-i18n-python[intl]"

from vue_i18n import datetime as d, number as n

These do not match Intl character for character

Everything around the format is a port: the argument shapes, the named formats, the fallback walk, the missing handling, the override merging and the cache. The formatting itself cannot be — Intl.DateTimeFormat and Intl.NumberFormat do not exist in Python, so babel stands in, and the two carry different CLDR data versions.

Month names and separators may differ from the browser. If a string must be byte-identical on both ends, format it on one end and send it.

Named formats

Declare them on the context, the same objects a Vue application passes:

short_date = {"year": "numeric", "month": "short", "day": "numeric"}

ctx = create_core_context(
    locale="de",
    fallback_locale="en",
    number_formats={
        "de": {"currency": {"style": "currency", "currency": "EUR"}},
        "en-US": {"currency": {"style": "currency", "currency": "USD"}},
        "ja": {"currency": {"style": "currency", "currency": "JPY"}},
    },
    datetime_formats={loc: {"short": short_date} for loc in ("de", "en-US", "ja")},
)

One format object, three locales — which is the whole reason these calls take a locale rather than a pattern:

n(ctx, 1234.5, "currency")              # '1.234,50 €'
n(ctx, 1234.5, "currency", "en-US")     # '$1,234.50'
n(ctx, 1234.5, "currency", "ja")        # '￥1,234'      - no minor unit for JPY

d(ctx, moment, "short")                 # '12. Aug. 2026'
d(ctx, moment, "short", "en-US")        # 'Aug 12, 2026'
d(ctx, moment, "short", "ja")           # '2026年8月12日'

Note the separator in 1.234,50 €: that is a non-breaking space before the symbol, not an ordinary one, which is the kind of detail the warning above is about. Compare with == rather than by eye.

A named format is looked up through the fallback chain, so a format defined only in en is found from a de context.

Call shapes

n(ctx, 1234.5)                                   # locale defaults
n(ctx, 1234.5, "currency")                       # a named format
n(ctx, 1234.5, "currency", "en")                 # named format, explicit locale
n(ctx, 1234.5, "currency", {"currency": "GBP"})  # named format with overrides
n(ctx, 1234.5, {"style": "percent"})             # options, no named format

d() takes the same shapes. Its value may be a datetime, a date, a POSIX timestamp in milliseconds (as Date does), or an ISO 8601 string.

Options that are honoured

Numbers — style (decimal, percent, currency), currency, useGrouping, minimumIntegerDigits, minimumFractionDigits, maximumFractionDigits, notation: "compact" with compactDisplay.

Dates — dateStyle and timeStyle (full, long, medium, short), the component options era, year, month, day, weekday, hour, minute, second, timeZoneName, plus hour12 and timeZone.

The component options are mapped onto a CLDR skeleton, which is what babel takes — so {"year": "numeric", "month": "short", "day": "numeric"} becomes yMMMd. That mapping is what lets a format object written for a Vue front end be read here unchanged.

Options that are ignored

Accepted and then dropped, because babel has nowhere to put them:

• numbers — localeMatcher, currencySign, signDisplay, unit, unitDisplay, roundingMode, roundingPriority, roundingIncrement, trailingZeroDisplay, minimumSignificantDigits, maximumSignificantDigits
• dates — localeMatcher, formatMatcher, calendar, numberingSystem, hourCycle, fractionalSecondDigits

Ask rather than discover:

from vue_i18n.runtime.number import unsupported_number_options
from vue_i18n.runtime.datetime import unsupported_datetime_options

unsupported_number_options({"style": "decimal", "signDisplay": "always"})   # {'signDisplay'}

Not supported

part=True (formatToParts) raises NotImplementedError. babel has no counterpart, and a caller asking for parts wants the structure — an approximation would be worse than a refusal.

Missing formats

Same as translate: a format name that resolves nowhere returns the name, or NOT_RESOLVED when the context was built with unresolving=True. A non-numeric value to n() warns and returns the empty string rather than raising, which is upstream's behaviour.