fixup! Rename (force|smart)_text to (force|smart)_str

Also Import lru_cache from seddable place

python/nav/compatibility.py

@@ -1,5 +1,9 @@
-# Django 4.0:
-# s/nav.compatibility \(import force_str\)/django.utils.encoding \1/'
+# Django 2.2 has only *_text, Django 3.2 has both *_text and *_str,
+# Django 4.0 has only *_str. These are imported so many places that
+# it is better to do it once, hence this file
+
+# When no longer supporting 2.2:
+# s/nav.compatibility \(import \w+_str\)/django.utils.encoding \1/
 try:
     from django.utils.encoding import force_str
 except ImoprtError:
@@ -9,3 +13,13 @@
     from django.utils.encoding import smart_str
 except ImoprtError:
     from django.utils.encoding import smart_text as smart_str
+
+# lru_cache isn't used that much but one application of sed is faster
+# than changing a block into a line three times.
+
+# When no longer supporting 2.2:
+# s/nav.compatibility import lru_cache/functools import lru_cache/
+try:
+    from functools import lru_cache
+except ImportError:
+    from django.utils.lru_cache import lru_cache