1 files changed, 3 insertions, 0 deletions
diff --git a/Lib/string.py b/Lib/string.py
index ef0787f52b..62e8f2f059 100644
--- a/Lib/string.py
+++ b/Lib/string.py
@@ -178,6 +178,9 @@ class Formatter:
         except ValueError:
             if 'format_string' in kwargs:
                 format_string = kwargs.pop('format_string')
+                import warnings
+                warnings.warn("Passing 'format_string' as keyword argument is "
+                              "deprecated", DeprecationWarning, stacklevel=2)
             else:
                 raise TypeError("format() missing 1 required positional "
                                 "argument: 'format_string'") from None