diff --git a/python/ray/tune/examples/ax_example.py b/python/ray/tune/examples/ax_example.py
index 26ad30cb9..019723f7a 100644
--- a/python/ray/tune/examples/ax_example.py
+++ b/python/ray/tune/examples/ax_example.py
@@ -41,7 +41,7 @@ def easy_objective(config, reporter):
     import time
     time.sleep(0.2)
     for i in range(config["iterations"]):
-        x = np.array([config.get(f"x{i+1}") for i in range(6)])
+        x = np.array([config.get("x{}".format(i + 1)) for i in range(6)])
         reporter(
             timesteps_total=i,
             hartmann6=hartmann6(x),