Add lm decode for the Python API. (#353)

* Add lm decode for the Python API.

* fix style.

* Fix LogAdd,

	Shouldn't double lm_log_prob when merge same prefix path

* sort the import alphabetically

@@ -116,6 +116,24 @@ def get_args():
     )
 
     parser.add_argument(
+        "--lm",
+        type=str,
+        default="",
+        help="""Used only when --decoding-method is modified_beam_search.
+        path of language model.
+        """,
+    )
+
+    parser.add_argument(
+        "--lm-scale",
+        type=float,
+        default=0.1,
+        help="""Used only when --decoding-method is modified_beam_search.
+        scale of language model.
+        """,
+    )
+
+    parser.add_argument(
         "--provider",
         type=str,
         default="cpu",
@@ -215,6 +233,8 @@ def main():
             feature_dim=80,
             decoding_method=args.decoding_method,
             max_active_paths=args.max_active_paths,
+            lm=args.lm,
+            lm_scale=args.lm_scale,
             hotwords_file=args.hotwords_file,
             hotwords_score=args.hotwords_score,
         )

@@ -17,11 +17,6 @@ void Hypotheses::Add(Hypothesis hyp) {
     hyps_dict_[key] = std::move(hyp);
   } else {
     it->second.log_prob = LogAdd<double>()(it->second.log_prob, hyp.log_prob);
-
-    if (it->second.lm_log_prob != 0 && hyp.lm_log_prob != 0) {
-      it->second.lm_log_prob =
-          LogAdd<double>()(it->second.lm_log_prob, hyp.lm_log_prob);
-    }
   }
 }
 

@@ -37,6 +37,7 @@ static void PybindOnlineRecognizerConfig(py::module *m) {
            py::arg("hotwords_score") = 0)
       .def_readwrite("feat_config", &PyClass::feat_config)
       .def_readwrite("model_config", &PyClass::model_config)
+      .def_readwrite("lm_config", &PyClass::lm_config)
       .def_readwrite("endpoint_config", &PyClass::endpoint_config)
       .def_readwrite("enable_endpoint", &PyClass::enable_endpoint)
       .def_readwrite("decoding_method", &PyClass::decoding_method)

@@ -5,6 +5,7 @@ from typing import List, Optional
 from _sherpa_onnx import (
     EndpointConfig,
     FeatureExtractorConfig,
+    OnlineLMConfig,
     OnlineModelConfig,
     OnlineParaformerModelConfig,
     OnlineRecognizer as _Recognizer,
@@ -46,6 +47,8 @@ class OnlineRecognizer(object):
         hotwords_file: str = "",
         provider: str = "cpu",
         model_type: str = "",
+        lm: str = "",
+        lm_scale: float = 0.1,
     ):
         """
         Please refer to
@@ -137,10 +140,22 @@ class OnlineRecognizer(object):
                 "Please use --decoding-method=modified_beam_search when using "
                 f"--hotwords-file. Currently given: {decoding_method}"
             )
+        
+        if lm and decoding_method != "modified_beam_search":
+            raise ValueError(
+                "Please use --decoding-method=modified_beam_search when using "
+                f"--lm. Currently given: {decoding_method}"
+            )
+        
+        lm_config = OnlineLMConfig(
+            model=lm,
+            scale=lm_scale,
+        )
 
         recognizer_config = OnlineRecognizerConfig(
             feat_config=feat_config,
             model_config=model_config,
+            lm_config=lm_config,
             endpoint_config=endpoint_config,
             enable_endpoint=enable_endpoint_detection,
             decoding_method=decoding_method,