Fix bug wrt change decoding strategy for bpe models (#7762) (#7764)

* Fix bug wrt change decoding strategy for bpe models



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---------

Signed-off-by: smajumdar <titu1994@gmail.com>
Co-authored-by: Somshubra Majumdar <titu1994@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

nemo/collections/asr/models/hybrid_rnnt_ctc_bpe_models.py

@@ -421,7 +421,9 @@ def change_decoding_strategy(self, decoding_cfg: DictConfig = None, decoder_type
             with open_dict(self.cfg.decoding):
                 self.cfg.decoding = decoding_cfg
 
+            self.cur_decoder = "rnnt"
             logging.info(f"Changed decoding strategy of the RNNT decoder to \n{OmegaConf.to_yaml(self.cfg.decoding)}")
+
         elif decoder_type == 'ctc':
             if not hasattr(self, 'ctc_decoding'):
                 raise ValueError("The model does not have the ctc_decoding module and does not support ctc decoding.")

tests/collections/asr/test_asr_hybrid_rnnt_ctc_model_bpe.py

@@ -307,3 +307,25 @@ def test_decoding_change(self, hybrid_asr_model):
         assert hybrid_asr_model.ctc_decoding.preserve_alignments is True
         assert hybrid_asr_model.ctc_decoding.compute_timestamps is True
         assert hybrid_asr_model.cur_decoder == "ctc"
+
+    @pytest.mark.skipif(
+        not NUMBA_RNNT_LOSS_AVAILABLE, reason='RNNTLoss has not been compiled with appropriate numba version.',
+    )
+    @pytest.mark.unit
+    def test_decoding_type_change(self, hybrid_asr_model):
+        assert isinstance(hybrid_asr_model.decoding.decoding, greedy_decode.GreedyBatchedRNNTInfer)
+
+        new_strategy = DictConfig({})
+        new_strategy.strategy = 'greedy'
+        new_strategy.greedy = DictConfig({'max_symbols': 10})
+        hybrid_asr_model.change_decoding_strategy(decoding_cfg=new_strategy, decoder_type='rnnt')
+        assert isinstance(hybrid_asr_model.decoding.decoding, greedy_decode.GreedyRNNTInfer)
+        assert hybrid_asr_model.cur_decoder == 'rnnt'
+
+        hybrid_asr_model.change_decoding_strategy(decoding_cfg=new_strategy, decoder_type='ctc')
+        assert isinstance(hybrid_asr_model.ctc_decoding, CTCBPEDecoding)
+        assert hybrid_asr_model.cur_decoder == 'ctc'
+
+        hybrid_asr_model.change_decoding_strategy(decoding_cfg=new_strategy, decoder_type='rnnt')
+        assert isinstance(hybrid_asr_model.decoding.decoding, greedy_decode.GreedyRNNTInfer)
+        assert hybrid_asr_model.cur_decoder == 'rnnt'

tests/collections/asr/test_asr_hybrid_rnnt_ctc_model_char.py

@@ -240,6 +240,28 @@ def test_decoding_change(self, hybrid_asr_model):
         assert hybrid_asr_model.ctc_decoding.preserve_alignments is True
         assert hybrid_asr_model.ctc_decoding.compute_timestamps is True
 
+    @pytest.mark.skipif(
+        not NUMBA_RNNT_LOSS_AVAILABLE, reason='RNNTLoss has not been compiled with appropriate numba version.',
+    )
+    @pytest.mark.unit
+    def test_decoding_type_change(self, hybrid_asr_model):
+        assert isinstance(hybrid_asr_model.decoding.decoding, greedy_decode.GreedyBatchedRNNTInfer)
+
+        new_strategy = DictConfig({})
+        new_strategy.strategy = 'greedy'
+        new_strategy.greedy = DictConfig({'max_symbols': 10})
+        hybrid_asr_model.change_decoding_strategy(decoding_cfg=new_strategy, decoder_type='rnnt')
+        assert isinstance(hybrid_asr_model.decoding.decoding, greedy_decode.GreedyRNNTInfer)
+        assert hybrid_asr_model.cur_decoder == 'rnnt'
+
+        hybrid_asr_model.change_decoding_strategy(decoding_cfg=new_strategy, decoder_type='ctc')
+        assert isinstance(hybrid_asr_model.ctc_decoding, CTCDecoding)
+        assert hybrid_asr_model.cur_decoder == 'ctc'
+
+        hybrid_asr_model.change_decoding_strategy(decoding_cfg=new_strategy, decoder_type='rnnt')
+        assert isinstance(hybrid_asr_model.decoding.decoding, greedy_decode.GreedyRNNTInfer)
+        assert hybrid_asr_model.cur_decoder == 'rnnt'
+
     @pytest.mark.unit
     def test_GreedyRNNTInferConfig(self):
         IGNORE_ARGS = ['decoder_model', 'joint_model', 'blank_index']