cast mesh zip to tuple for consistent behavior

Author: winglian

src/accelerate/utils/dataclasses.py

@@ -2999,7 +2999,7 @@ def active_mesh_dims(self):
 
     def build_device_mesh(self, device_type: str):
         mesh = self.get_mesh()
-        if len(list(mesh)) == 0:
+        if not mesh:
             return
         mesh_dim_names, mesh_shape = mesh
         device_mesh = torch.distributed.init_device_mesh(
@@ -3028,7 +3028,7 @@ def get_mesh(self) -> tuple[tuple[int, ...], tuple[str, ...]]:
             mesh_dims.items(),
             key=lambda x: (mesh_order.index(x[0])),
         )
-        return zip(*sorted_items)
+        return tuple(zip(*sorted_items))
 
     def __post_init__(self):
         # Basic size validation