Selector Functions

Selector functions allow you to provide away to determine a user’s locale and timezone based on pre-existing information in an application. These functions can be set on the constructor of ~Babel object, when initializing the app with the babel extension; ~Babel.init_app, or by directly setting ~Babel.locale_selector and/or ~Babel.timezone_selector. These functions are then passed to the constructor for ~QuartBabelMiddleware.

If any of these methods return None the extension will automatically fall back to what’s in the config. If you need to switch the language or timezone between a request, you can refresh_locale() and refresh_timezone() respectively.

The selector functions must be coroutines.

Locale Selector:

The locale selector must accept an ASGI request object, which is different ~Quart.request. The ~QuartBabelMiddleware will pass the ASGI request object to the locale selector function when called. Furthermore, the locale selector needs to return a string or Babel.Locale object.

You can also call use select_locale_by_request() to fallback on if no information is available.

Locale Selector Example

from quart import Quart, g, request
from quart_babel import Babel, select_locale_by_request
from quart_babel.typing import ASGIRequest

app = Quart(__name__)

async def get_locale(request: ASGIRequest) -> str:
   # if a user is logged in, use the locale from the user settings
   user = getattr(g, 'user', None)
   if user is not None:
       return user.locale
   # otherwise select the user by the ASGI request object.
   return await select_locale_by_request(request)

babel(app, locale_selector=get_locale)

Timezone Selector:

The timezone selector must accept an ASGI request object, which is different ~Quart.request. The ~QuartBabelMiddleware will pass the ASGI request object to the locale selector function when called. Furthermore, the locale selector needs to return a string.

You can also call use select_timezone_by_request() to fallback on if no information is available.

Timezone Selector Example

import asyncio
from quart import Quart, g, request
from quart_babel import Babel, select_locale_by_request
from quart_babel.typing import ASGIRequest

app = Quart(__name__)

async def get_timezone(request: ASGIRequest) -> str | None:
   # if a user is logged in, use the locale from the user settings
   user = getattr(g, 'user', None)
   if user is not None:
       return user.timezone
   # otherwise use default timezone by returning None.
   return None

babel(app, timezone_selector=get_timezone)

Note

The examples above assumes that the current user is stored on the Quart.g object.