Python flask web application with multilanguages support by host and prefix

Question

I have one server with flask application instance and have several domain which mapped to this server by DNS.

My site must support several languages by host and pref

Answer 1

My own solution:

from flask import Flask, g, render_template, redirect, request


app = Flask(__name__)

default_language = 'en'
language_urls = {
    'en': 'mysite.com',
    'fr': 'mysite.com/fr',
    'ru': 'mysite.ru',
    'by': 'mysite.ru/by',
}
languages = ','.join(language_urls.keys())


def get_language_by_request(request_host, request_path):
    '''
    Looking bad, but work.
    I cab't use request.view_args there,
    because this can't detect language for 404 pages
    like mysite.com/fr/unknown-page
    '''
    request_host_path = request_host + request_path
    request_paths = request_host_path.split('/', 2)
    if (len(request_paths) > 1 and request_paths[1] in language_urls.keys()):
        request_language_prefix = request_paths[1]
        return request_language_prefix
    for language, url in language_urls.items():
        host_prefix = url.split('/')
        if len(host_prefix) == 1:
            host, = host_prefix
            if request_host == host:
                return language
    return default_language


def get_language_url_parameter_value(language, request_host):
    host_prefix = language_urls[language]
    if host_prefix == request_host:
        return None
    return language


def get_redirection_url_by_request(request_host, request_path, request_url):
    '''
    Looking bad, but work.
    I cab't use request.view_args there,
    because this can't detect language for 404 pages
    like mysite.com/fr/unknown-page
    '''
    request_host_path = request_host + request_path
    request_paths = request_host_path.split('/', 2)
    request_language_prefix = None
    if (len(request_paths) > 1 and request_paths[1] in language_urls.keys()):
        request_language_prefix = request_paths[1]
    hosts = []
    for language, url in language_urls.items():
        host_prefix = url.split('/')
        if len(host_prefix) == 1:
            host, = host_prefix
            language_prefix = None
        else:
            host, language_prefix = host_prefix
        if request_host == host and request_language_prefix == language_prefix:
            return None
        hosts.append(host)
    if request_host not in hosts:
        return None
    if request_language_prefix:
        request_host_prefix = request_host + '/' + request_language_prefix
        host_prefix = language_urls[request_language_prefix]
        return request_url.replace(request_host_prefix, host_prefix)
    return None


@app.url_defaults
def set_language_in_url(endpoint, values):
    if '_lang' not in values and hasattr(g, 'language_url_value'):
        values['_lang'] = g.language_url_value


@app.url_value_preprocessor
def get_language_from_url(endpoint, values):
    g.language = get_language_by_request(request.host, request.path)
    g.language_url_value = get_language_url_parameter_value(g.language, request.host)
    if values and '_lang' in values:
        del values['_lang']


@app.before_request
def check_language_redirection():
    redirection_url = get_redirection_url_by_request(request.host, request.path, request.url)
    return redirect(redirection_url) if redirection_url else None


@app.route('/')
@app.route('//' % languages)
def home():
    return render_template('home.html')


@app.route('/other/')
@app.route('//other/' % languages)
def other():
    return render_template('other.html')

I don't use blueprints there because I also use flask-login and I can't set several login pages with different languages for each blueprint. For example if page required login, flask redirect me to login page and I must update language for this page. Also login pages can't be as mysite.com/login, mysite.com/fr/login and etc without several redirections.

UPD: I can't use request.view_args for detect language or redirection, because on this case I can't detect language for error pages as mysite.com/fr/wrong-page-there (can't detect endpoint and view_args). To avoid this problem I can use hask: add url rule as // and raise 404 error there.