[Fix] Fix a bug when module is missing in low version of bitsandbytes (…

…#1388)

mmengine/optim/optimizer/builder.py

@@ -132,6 +132,10 @@ def register_sophia_optimizers() -> List[str]:
 def register_bitsandbytes_optimizers() -> List[str]:
     """Register optimizers in ``bitsandbytes`` to the ``OPTIMIZERS`` registry.
 
+    In the `bitsandbytes` library, optimizers that have the same name as the
+    default optimizers in PyTorch are prefixed with ``bnb_``. For example,
+    ``bnb_Adagrad``.
+
     Returns:
         List[str]: A list of registered optimizers' name.
     """
@@ -141,16 +145,14 @@ def register_bitsandbytes_optimizers() -> List[str]:
     except ImportError:
         pass
     else:
-        for module_name in [
-                'AdamW8bit', 'Adam8bit', 'Adagrad8bit', 'PagedAdam8bit',
-                'PagedAdamW8bit', 'LAMB8bit', 'LARS8bit', 'RMSprop8bit',
-                'Lion8bit', 'PagedLion8bit', 'SGD8bit'
-        ]:
-            _optim = getattr(bnb.optim, module_name)
-            if inspect.isclass(_optim) and issubclass(_optim,
-                                                      torch.optim.Optimizer):
-                OPTIMIZERS.register_module(module=_optim)
-                dadaptation_optimizers.append(module_name)
+        optim_classes = inspect.getmembers(
+            bnb.optim, lambda _optim: (inspect.isclass(_optim) and issubclass(
+                _optim, torch.optim.Optimizer)))
+        for name, optim_cls in optim_classes:
+            if name in OPTIMIZERS:
+                name = f'bnb_{name}'
+            OPTIMIZERS.register_module(module=optim_cls, name=name)
+            dadaptation_optimizers.append(name)
     return dadaptation_optimizers