Replace string_concat() with format_lazy()

On Django 1.11 django.utils.translation.string_concat() is
deprecated in favor of django.utils.text.format_lazy()
and it has been removed on Django 2.1

orchestra/contrib/services/helpers.py

@@ -1,3 +1,7 @@
+from django.utils.text import format_lazy
+from django.utils.translation import ugettext_lazy
+
+
 def get_chunks(porders, ini, end, ix=0):
     if ix >= len(porders):
         return [[ini, end, []]]
@@ -130,3 +134,16 @@ def compensate(order, compensations):
     for __, compensation in ordered_intersections:
         remaining_compensations.append(compensation)
     return remaining_compensations, applied_compensations
+
+
+def get_rate_methods_help_text(rate_class):
+    method_help_texts = [
+        format_lazy('{}' * 4, *['<br>&nbsp;&nbsp;', method.verbose_name, ': ', method.help_text])
+            for method in rate_class.get_methods().values()
+    ]
+    prefix = ugettext_lazy("Algorithm used to interprete the rating table.")
+    help_text_items = [prefix] + method_help_texts
+    return format_lazy(
+        '{}' * len(help_text_items),
+        *help_text_items
+    )

orchestra/contrib/services/models.py

@@ -1,18 +1,20 @@
 import calendar
 import decimal
+from orchestra.contrib.services import helpers
 
 from django.contrib.contenttypes.models import ContentType
 from django.db import models
 from django.apps import apps
 from django.utils.functional import cached_property
 from django.utils.module_loading import autodiscover_modules
-from django.utils.translation import string_concat, ugettext_lazy as _
+from django.utils.translation import ugettext_lazy as _
 
 from orchestra.core import caches, validators
 from orchestra.utils.python import import_class
 
 from . import settings
 from .handlers import ServiceHandler
+from .helpers import get_rate_methods_help_text
 
 
 autodiscover_modules('handlers')
@@ -145,13 +147,12 @@ class Service(models.Model):
             (ANUAL, _("Anual data")),
         ),
         default=BILLING_PERIOD)
-    rate_algorithm = models.CharField(_("rate algorithm"), max_length=64,
+    rate_algorithm = models.CharField(
+        _("rate algorithm"), max_length=64,
         choices=rate_class.get_choices(),
         default=rate_class.get_default(),
-        help_text=string_concat(_("Algorithm used to interprete the rating table."), *[
+        help_text=get_rate_methods_help_text(rate_class),
-            string_concat('<br>&nbsp;&nbsp;', method.verbose_name, ': ', method.help_text)
+    )
-                for name, method in rate_class.get_methods().items()
-        ]))
     on_cancel = models.CharField(_("on cancel"), max_length=16,
         help_text=_("Defines the cancellation behaviour of this service."),
         choices=(

orchestra/core/__init__.py

@@ -1,4 +1,4 @@
-from django.utils.translation import string_concat
+from django.utils.text import format_lazy
 
 from ..utils.python import AttrDict
 
@@ -36,7 +36,8 @@ class Register(object):
         if 'verbose_name' not in kwargs:
             raise KeyError("%s verbose_name is required for views" % view_name)
         if 'verbose_name_plural' not in kwargs:
-            kwargs['verbose_name_plural'] = string_concat(kwargs['verbose_name'], 's')
+            kwargs['verbose_name_plural'] = format_lazy('{}' * 2, *[kwargs['verbose_name'], 's'])
+
         self.register(view_name, **kwargs)
 
     def get(self, *args):