Don't forget the i18n use case

Posted Feb 3, 2025 0:29 UTC (Mon) by zahlman (guest, #175387)
In reply to: Don't forget the i18n use case by mgedmin
Parent article: A revamped Python string-formatting proposal

Neat idea. I guess the implementation for your helper is something like:

from itertools import count
from gettext import gettext

def escape_braces(s: str):
    return s.replace('{', '{{').replace('}', '}}')

def _lookup_pieces(t: Template):
    placeholders = (f'{i}' for i in count())
    for item in t:
        if isinstance(t, Interpolation): yield next(placeholders)
        else: yield escape_braces(t)

def _(t: Template):
    lookup = ''.join(_lookup_pieces(t))
    interpolations = (i.value for i in t if isinstance(i, Interpolation))
    return gettext(lookup).format(*interpolations)

That is: we need to normalize the Template into a canonical string that can be looked up in the usual way - and if we follow appropriate conventions (using only numeric placeholders, and following standard brace-escaping convention) in the localized strings, the result will be suitable for use with str.format. We want to look up a string that depends only on the literal parts of the t-string - not on either the values that will be interpolated nor the expressions used to compute them. So e.g. t"Hello, {firstname} {lastname}!" and t"Hello, {firstname} {lastname.capitalize()}!" should both map to a lookup string "Hello, {0} {1}!", which can then retrieve a localized string like "{1}　{0}ーさん、今日は！".

But it should be noted that none of this helps if the interpolated values need to be localized as well...