Do not implicitly mutate Catalog when accessing its properties

diff --git a/babel/messages/catalog.py b/babel/messages/catalog.py
index f84a5bd1b389ff2b1f4fff4202722103dab54bb7..954dad0e3d09cc475e9b68f9f4e678915ea4bb54 100644 (file)
--- a/babel/messages/catalog.py
+++ b/babel/messages/catalog.py
@@ -613,7 +613,7 @@ class Catalog:
             num = 2
             if self.locale:
                 num = get_plural(self.locale)[0]
-            self._num_plurals = num
+            return num
         return self._num_plurals
 
     @property
@@ -632,7 +632,7 @@ class Catalog:
             expr = '(n != 1)'
             if self.locale:
                 expr = get_plural(self.locale)[1]
-            self._plural_expr = expr
+            return expr
         return self._plural_expr
 
     @property