bpo-28692: Deprecate using non-integer value for selecting a plural form in gettext. (#507)

diff --git a/Lib/gettext.py b/Lib/gettext.py
index 57d2c74..aa1d555 100644
--- a/Lib/gettext.py
+++ b/Lib/gettext.py
@@ -164,6 +164,10 @@
     except TypeError:
         raise TypeError('Plural value must be an integer, got %s' %
                         (n.__class__.__name__,)) from None
+    import warnings
+    warnings.warn('Plural value must be an integer, got %s' %
+                  (n.__class__.__name__,),
+                  DeprecationWarning, 4)
     return n
 
 def c2py(plural):
diff --git a/Lib/test/test_gettext.py b/Lib/test/test_gettext.py
index a852443..7bfe747 100644
--- a/Lib/test/test_gettext.py
+++ b/Lib/test/test_gettext.py
@@ -443,9 +443,12 @@
         f = gettext.c2py('n != 1')
         self.assertEqual(f(1), 0)
         self.assertEqual(f(2), 1)
-        self.assertEqual(f(1.0), 0)
-        self.assertEqual(f(2.0), 1)
-        self.assertEqual(f(1.1), 1)
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(f(1.0), 0)
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(f(2.0), 1)
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(f(1.1), 1)
         self.assertRaises(TypeError, f, '2')
         self.assertRaises(TypeError, f, b'2')
         self.assertRaises(TypeError, f, [])