Fixed #26866 -- Added format_lazy function

Added format_lazy function to django.utils.text module.
Useful when dealing with relative complex lazy string concatenations
(e.g. in urls.py when translating urls in regular expressions).

1 files changed, 12 insertions, 1 deletions

diff --git a/django/utils/text.py b/django/utils/text.py
index f51113b483..3b8fc581bf 100644
--- a/django/utils/text.py
+++ b/django/utils/text.py
@@ -7,7 +7,9 @@ from io import BytesIO
 
 from django.utils import six
 from django.utils.encoding import force_text
-from django.utils.functional import SimpleLazyObject, keep_lazy, keep_lazy_text
+from django.utils.functional import (
+    SimpleLazyObject, keep_lazy, keep_lazy_text, lazy,
+)
 from django.utils.safestring import SafeText, mark_safe
 from django.utils.six.moves import html_entities
 from django.utils.translation import pgettext, ugettext as _, ugettext_lazy
@@ -434,3 +436,12 @@ def camel_case_to_spaces(value):
     trailing whitespace.
     """
     return re_camel_case.sub(r' \1', value).strip().lower()
+
+
+def _format_lazy(format_string, *args, **kwargs):
+    """
+    Apply str.format() on 'format_string' where format_string, args,
+    and/or kwargs might be lazy.
+    """
+    return format_string.format(*args, **kwargs)
+format_lazy = lazy(_format_lazy, six.text_type)