python gettext different languages at same time

Question

I'm using flask, pybabel for i18n. Sometimes I need to send emails to my users. And I want to send email in their own language. Language code stores in databases so the problem is to translate template with right language. Here is part of my sending function:

            lang = user.get_lang()
            subject = _('Subject')
            for user in users:
                if user.email:
                        body = render_template('emails/template.eml', user=user)
                        recipients = [user.email]
                        msg = Message(subject, html=body, recipients=recipients)
                        conn.send(msg)

And example of template:

{{ _('Hi {name}. How are you?').format(user.name) }}

All I need is something like set_langauge(lang) which I can call before each template render. How can I do it?

Thanks.

Answer 1

I have next render_template function for emails:

def render_template(template_name_or_list, **context):

    # get  request context
    ctx = _request_ctx_stack.top

    # check request context
    # if function called without request context
    # then call with `test_tequest_context`
    # this because I send email from celery tasks
    if ctx is None:
        with current_app.test_request_context():
            return render_template(template_name_or_list, **context)

    # I have specific locale detection (from url)
    # and also use `lang` variable in template for `url_for` links
    # so you can just pass language parameter without context parameter
    # and always set `babel_locate` with passed language
    locale = getattr(ctx, 'babel_locale', None)
    if locale is None:
        ctx.babel_locale = Locale.parse(context['lang'])

    # render template without additinals context processor
    # because I don't need this context for emails
    # (compare with default flask `render_template` function)
    return _render(ctx.app.jinja_env.get_or_select_template(
        template_name_or_list), context, ctx.app)

So if you need just change language in request context use next code (see get_locale):

def set_langauge(lang)
    ctx = _request_ctx_stack.top
    ctx.babel_locale = Locale.parse(lang)

Answer 2

Thanks to @tbicr I ended up with this solution.

In my app.py I have set_locale function:

from flask import _request_ctx_stack as ctx_stack
# ...
def set_locale(lang):
    ctx = ctx_stack.top
    ctx.babel_locale = lang
# ...

and I call it before rendering email template.

The problem was I need to send emails to many users with different languages at the same time:

with app.test_request_context():
    with mail.connect() as conn:
        for user in users:
            set_locale(user.get_lang())
            subject = _(u'Best works').format(get_month_display(month))
            body = render_template('emails/best_works.eml'
                recipients = [user.email]
                msg = Message(subject, html=body, recipients=recipients)
                conn.send(msg)

and when I call set_locale first time the value of locale was cached and all emails were rendered with language of first user.

The solution is to call flaskext.babel.refresh each time after set_locale