add guards

Author: winglian

src/accelerate/accelerator.py

@@ -448,8 +448,9 @@ def __init__(
             **kwargs,
         )
 
-        self._build_torch_device_mesh(self.parallelism_config)
-        self.parallelism_config.validate_accelerator(self)
+        if self.parallelism_config:
+            self._build_torch_device_mesh(self.parallelism_config)
+            self.parallelism_config.validate_accelerator(self)
 
         self.fp8_enabled = self.state.mixed_precision == "fp8" or mixed_precision == "fp8"
 

src/accelerate/utils/dataclasses.py

@@ -2998,7 +2998,10 @@ def active_mesh_dims(self):
         return self.dp_dim_names + self.non_dp_dim_names
 
     def build_device_mesh(self, device_type: str):
-        mesh_dim_names, mesh_shape = self.get_mesh()
+        mesh = self.get_mesh()
+        if not mesh:
+            return
+        mesh_dim_names, mesh_shape = mesh
         device_mesh = torch.distributed.init_device_mesh(
             device_type,
             mesh_shape,