fix(quantization): accept QuantizeAlgorithmConfig in get_modelike_from_algo_cfg

CHANGELOG.rst

@@ -31,6 +31,7 @@ Changelog
 **Bug Fixes**
 
 - Fix Megatron-Core HF importer to load fused ``TELayerNormColumnParallelLinear.layer_norm_weight`` from HF for GPT-family models (Qwen3 etc.) under ``--export-default-te-spec``. Importer now prefers per-context keys ``fused_input_layernorm`` / ``fused_pre_mlp_layernorm`` (fallback ``fused_norm`` for Nemotron-H backward compatibility); ``mcore_qwen.py`` provides the new rules. Without this fix, post-prune MMLU sat at chance.
+- Fix ``QuantizeAlgorithmConfig`` instances being rejected with ``ValueError`` when passed as the ``algorithm`` in a quantization config (e.g. ``cfg["algorithm"] = mtq.MaxCalibConfig(...)``). Such instances are now accepted, consistent with the ``algorithm`` field's type annotation.
 
 0.44 (2026-05-14)
 ^^^^^^^^^^^^^^^^^

modelopt/torch/quantization/mode.py

@@ -16,7 +16,7 @@
 """This module contains the mode descriptor for the quantization mode."""
 
 from abc import abstractmethod
-from collections.abc import Callable
+from collections.abc import Callable, Mapping
 
 from modelopt.torch.opt.config import ModeloptBaseConfig
 from modelopt.torch.opt.conversion import ModelLikeModule
@@ -374,7 +374,9 @@ def get_modelike_from_algo_cfg(algo_cfg: QuantizeAlgoCfgType) -> ModeConfigList:
         return [get_modelike_from_algo_cfg(c)[0] for c in algo_cfg]
     if algo_cfg is None or isinstance(algo_cfg, str):
         algo_name, algo_cfg = algo_cfg, {}
-    elif isinstance(algo_cfg, dict):
+    elif isinstance(algo_cfg, Mapping):
+        # Normalize any mapping (incl. ModeloptBaseConfig instances) to a plain dict.
+        algo_cfg = dict(algo_cfg)
         algo_name = algo_cfg["method"]
     else:
         raise ValueError(f"Invalid config type: {type(algo_cfg)}")

tests/unit/torch/quantization/test_mode.py

@@ -19,11 +19,16 @@
 
 from modelopt.torch.opt.config import ModeloptField
 from modelopt.torch.opt.mode import _ModeRegistryCls
-from modelopt.torch.quantization.config import QuantizeAlgorithmConfig
+from modelopt.torch.quantization.config import (
+    MaxCalibConfig,
+    QuantizeAlgorithmConfig,
+    SmoothQuantCalibConfig,
+)
 from modelopt.torch.quantization.mode import (
     BaseCalibrateModeDescriptor,
     CalibrateModeRegistry,
     QuantizeModeRegistry,
+    get_modelike_from_algo_cfg,
 )
 
 
@@ -60,3 +65,20 @@ def config_class(self) -> QuantizeAlgorithmConfig:
         @CalibrateModeRegistry.register_mode
         class TestIncorrectCalibrateModeDescriptor:
             pass
+
+
+def test_get_modelike_from_algo_cfg_accepts_config_instance():
+    """Regression test for GitHub issue #201.
+
+    A ``QuantizeAlgorithmConfig`` instance passed as the ``algorithm`` config is
+    normalized to a dict and accepted, instead of raising ``ValueError``.
+    """
+    mode_name, algo_cfg = get_modelike_from_algo_cfg(MaxCalibConfig(distributed_sync=False))[0]
+    assert mode_name == "max_calibrate"
+    assert isinstance(algo_cfg, dict)
+    assert algo_cfg["distributed_sync"] is False
+    MaxCalibConfig(**algo_cfg)
+
+    modes = get_modelike_from_algo_cfg([MaxCalibConfig(), SmoothQuantCalibConfig()])
+    assert [name for name, _ in modes] == ["max_calibrate", "smoothquant_calibrate"]
+    assert all(isinstance(cfg, dict) for _, cfg in modes)

tests/unit/torch/quantization/test_quantize_cpu.py

@@ -32,7 +32,7 @@
 import modelopt.torch.opt as mto
 import modelopt.torch.quantization as mtq
 from modelopt.torch.quantization.calib import MaxCalibrator
-from modelopt.torch.quantization.config import QuantizerAttributeConfig
+from modelopt.torch.quantization.config import MaxCalibConfig, QuantizerAttributeConfig
 from modelopt.torch.quantization.conversion import set_quantizer_attributes_full
 from modelopt.torch.quantization.nn.modules.tensor_quantizer import (
     SequentialQuantizer,
@@ -167,6 +167,18 @@ def forward_loop():
     mtq.quantize(model, mtq.INT8_DEFAULT_CFG, forward_loop=forward_loop)
 
 
+def test_quantize_accepts_algo_config_instance_end_to_end():
+    """Regression test for GitHub issue #201.
+
+    A ``QuantizeAlgorithmConfig`` instance set as ``config["algorithm"]`` must not
+    raise ``ValueError`` through the full quantize/calibrate flow.
+    """
+    quant_config = copy.deepcopy(mtq.INT8_DEFAULT_CFG)
+    quant_config["algorithm"] = MaxCalibConfig(distributed_sync=False)
+    model = SimpleLinear()
+    quantize_model_and_forward(model, quant_config, [model.get_input() for _ in range(2)])
+
+
 def test_custom_calib_config():
     model_ref = SimpleLinear()
     model_ref = mtq.quantize(