Empty index `[0,,1]` robust device selection (#16631)

ultralytics/utils/torch_utils.py

@@ -170,6 +170,8 @@ def select_device(device="", batch=0, newline=False, verbose=True):
     elif device:  # non-cpu device requested
         if device == "cuda":
             device = "0"
+        if "," in device:
+            device = ",".join([x for x in device.split(",") if x])  # remove sequential commas, i.e. "0,,1" -> "0,1"
         visible = os.environ.get("CUDA_VISIBLE_DEVICES", None)
         os.environ["CUDA_VISIBLE_DEVICES"] = device  # set environment variable - must be before assert is_available()
         if not (torch.cuda.is_available() and torch.cuda.device_count() >= len(device.split(","))):
@@ -191,7 +193,7 @@ def select_device(device="", batch=0, newline=False, verbose=True):
             )
 
     if not cpu and not mps and torch.cuda.is_available():  # prefer GPU if available
-        devices = device.split(",") if device else "0"  # range(torch.cuda.device_count())  # i.e. 0,1,6,7
+        devices = device.split(",") if device else "0"  # i.e. "0,1" -> ["0", "1"]
         n = len(devices)  # device count
         if n > 1:  # multi-GPU
             if batch < 1: