From 5c192954b7864c34721608f9d9ae40062ee595b3 Mon Sep 17 00:00:00 2001
From: Thomas Baumann <39156931+brownbaerchen@users.noreply.github.com>
Date: Mon, 8 Jun 2026 14:59:04 +0200
Subject: [PATCH 1/2] Tell people what device they tried to use if it's not
 available

---
 heat/core/devices.py       | 4 +++-
 tests/core/test_devices.py | 7 +++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/heat/core/devices.py b/heat/core/devices.py
index 83a2be05c6..ff4408764e 100644
--- a/heat/core/devices.py
+++ b/heat/core/devices.py
@@ -189,7 +189,9 @@ def sanitize_device(device: Optional[Union[str, Device]] = None) -> Device:
     try:
         return __device_mapping[device.strip().lower()]
     except (AttributeError, KeyError, TypeError):
-        raise ValueError(f"Unknown device, must be one of {', '.join(__device_mapping.keys())}")
+        raise ValueError(
+            f"Unknown device {device!r}, must be one of {', '.join(__device_mapping.keys())}"
+        )
 
 
 def use_device(device: Optional[Union[str, Device]] = None) -> None:
diff --git a/tests/core/test_devices.py b/tests/core/test_devices.py
index 0d76ae053c..c8a09c518b 100644
--- a/tests/core/test_devices.py
+++ b/tests/core/test_devices.py
@@ -1,5 +1,6 @@
 import os
 import unittest
+import pytest
 
 import heat as ht
 from heat.testing.basic_test import TestCase
@@ -72,3 +73,9 @@ def test_set_default_device_gpu(self):
             ht.use_device("fpu")
         with self.assertRaises(ValueError):
             ht.use_device(1)
+
+
+def test_unknown_device_error_message():
+    device_name = "Sauron's Eye"
+    with pytest.raises(ValueError, match=device_name):
+        ht.use_device(device_name)

From 5efb02888acfffab10cb58274506b40c6c3d9a6f Mon Sep 17 00:00:00 2001
From: Thomas Saupe <39156931+brownbaerchen@users.noreply.github.com>
Date: Wed, 10 Jun 2026 09:35:32 +0200
Subject: [PATCH 2/2] Update heat/core/devices.py

Co-authored-by: Michael Tarnawa <18899420+mtar@users.noreply.github.com>
---
 heat/core/devices.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/heat/core/devices.py b/heat/core/devices.py
index ff4408764e..0fb32a9282 100644
--- a/heat/core/devices.py
+++ b/heat/core/devices.py
@@ -190,7 +190,7 @@ def sanitize_device(device: Optional[Union[str, Device]] = None) -> Device:
         return __device_mapping[device.strip().lower()]
     except (AttributeError, KeyError, TypeError):
         raise ValueError(
-            f"Unknown device {device!r}, must be one of {', '.join(__device_mapping.keys())}"
+            f"Unknown device {device!r}, must be one of {tuple(__device_mapping.keys())}"
         )