simplify accelerate main process detection

src/lerobot/scripts/lerobot_train.py

@@ -163,24 +163,15 @@ def train(cfg: TrainPipelineConfig, accelerator: Callable | None = None):
     """
     cfg.validate()
 
-    # Check if this is the main process
-    # Use LOCAL_RANK environment variable (set by accelerate) for reliable detection
-    local_rank = int(os.environ.get("LOCAL_RANK", -1))
-    if local_rank == -1:
-        # No LOCAL_RANK, check accelerator object or assume main process
-        is_main_process = not accelerator or (hasattr(accelerator, 'is_main_process') and accelerator.is_main_process)
-    else:
-        # LOCAL_RANK is set, main process is rank 0
-        is_main_process = local_rank == 0
-
-    if accelerator and not is_main_process:
-        # Disable WandB and logging on non-main processes.
-        cfg.wandb.enable = False
+    # Determine if this is the main process (for logging and checkpointing)
+    # When using accelerate, only the main process should log to avoid duplicate outputs
+    is_main_process = accelerator.is_main_process if accelerator else True
 
+    # Only log on main process
     if is_main_process:
         logging.info(pformat(cfg.to_dict()))
 
-    # Only create WandB logger on main process
+    # Initialize wandb only on main process
     if cfg.wandb.enable and cfg.wandb.project and is_main_process:
         wandb_logger = WandBLogger(cfg)
     else: