[FIXED] django format_html not working with string_concat

Issue

I am trying to display a two line error message to a user. All attempts I have made have failed and I cannot figure this out, despite searching SO & google.

The error I am getting is:

Exception Type: IndexError

Exception Value: tuple index out of range

The issue seems to be the use of the format_html() with the string_concat().

Here is my python code:

from django.utils import translation
from django.utils.html import format_html
from django.utils.translation import string_concat
from django.utils.translation import ugettext_lazy as _
....
if not request.user.is_staff and language_versions_num_enabled > max_languages:
    error_message = format_html(
        string_concat(
            _(u'You are only permitted <b>{}</b> <u>enabled</u> Language Versions for the selected <b>{}</b> subscription plan.'),
            ' <icon class="fa fa-frown-o icon_size26 icon_padding"></icon>',
            '<br /><br />',
            _(u'Either select a different subscription plan or disable <b>{}</b> of your <b>{}</b> <u>enabled</u> Language Versions.'.format(max_languages, stripe_plan['title'], language_versions_num_enabled-max_languages, language_versions_num_enabled))
        )
    )
    messages.add_message(request, messages.ERROR, error_message)
else:

I am really hoping someone can point out what I am doing wrong here.

EDIT

I am using django 1.10 and python 3.5.2.

Here is the stack trace:

Environment:


Request Method: POST
Request URL: http://127.0.0.1:8000/subscription/subscription/

Django Version: 1.10.5
Python Version: 3.5.2
Installed Applications:
('django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.humanize',
 'django.contrib.messages',
 'django.contrib.sessions',
 'django.contrib.sites',
 'django.contrib.sitemaps',
 'django.contrib.staticfiles',
 'admin_honeypot',
 'axes',
 'rest_framework',
 'rest_framework.authtoken',
 'captcha',
 'my_app.contact',
 'djstripe',
 'my_app.common',
 'my_app.users',
 'my_app.core',
 'imagekit',
 'parsley',
 'registration',
 'templatetag_handlebars',
 'settings_context_processor',
 'crispy_forms',
 'lockdown',
 'rosetta',
 'raven.contrib.django.raven_compat')
Installed Middleware:
('raven.contrib.django.middleware.SentryMiddleware',
 'django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'my_app.users.middleware.LocaleOverrideMiddleware',
 'django.middleware.locale.LocaleMiddleware',
 'my_app.users.middleware.AdminLocaleMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware',
 'lockdown.middleware.LockdownMiddleware')



Traceback:

File "C:\Users\laptop\desktop\my_app\env3\lib\site-packages\django\core\handlers\exception.py" in inner
  39.             response = get_response(request)

File "C:\Users\laptop\desktop\my_app\env3\lib\site-packages\django\core\handlers\base.py" in _legacy_get_response
  249.             response = self._get_response(request)

File "C:\Users\laptop\desktop\my_app\env3\lib\site-packages\django\core\handlers\base.py" in _get_response
  187.                 response = self.process_exception_by_middleware(e, request)

File "C:\Users\laptop\desktop\my_app\env3\lib\site-packages\django\core\handlers\base.py" in _get_response
  185.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "C:\Users\laptop\desktop\my_app\env3\lib\site-packages\django\contrib\auth\decorators.py" in _wrapped_view
  23.                 return view_func(request, *args, **kwargs)

File "C:\Users\laptop\desktop\my_app\env3\lib\site-packages\django\views\decorators\http.py" in inner
  40.             return func(request, *args, **kwargs)

File "C:\Users\laptop\desktop\my_app\my_app\core\decorators.py" in wrapper
  21.             return f(request, *args, **kwargs)

File "C:\Users\laptop\desktop\my_app\my_app\core\views\user_settings_views.py" in subscription
  402.                                 _(u'Either select a different subscription plan or disable <b>{}</b> of your <b>{}</b> <u>enabled</u> Language Versions.'.format(max_languages, stripe_plan['title'], language_versions_num_enabled-max_languages, language_versions_num_enabled))

File "C:\Users\laptop\desktop\my_app\env3\lib\site-packages\django\utils\html.py" in format_html
  106.     return mark_safe(format_string.format(*args_safe, **kwargs_safe))

File "C:\Users\laptop\desktop\my_app\env3\lib\site-packages\django\utils\functional.py" in __wrapper__
  112.                 return getattr(res, method_name)(*args, **kw)

Exception Type: IndexError at /subscription/subscription/
Exception Value: tuple index out of range

Solution

You put format in the wrong place. Try this:

error_message = format_html(
    string_concat(
        _(u'You are only permitted <b>{}</b> <u>enabled</u> Language Versions for the selected <b>{}</b> subscription plan.'),
        ' <icon class="fa fa-frown-o icon_size26 icon_padding"></icon>',
        '<br /><br />',
        _(u'Either select a different subscription plan or disable <b>{}</b> of your <b>{}</b> <u>enabled</u> Language Versions.')
    ).format(max_languages, stripe_plan['title'], language_versions_num_enabled-max_languages, language_versions_num_enabled)
)

Answered By - munsu