fix(asr): make DynamicLengthTensor indexing Python 3.10-compatible (#15797)

[gauravbyte]

What does this PR do ?

Fixes a SyntaxError on Python 3.10 in nemo/collections/asr/parts/utils/streaming_utils.py.

DynamicLengthTensor.append_no_checks_ indexed a tensor using a PEP 646 starred
expression placed directly inside a subscript:

shifted_indices = shifted_indices[..., *[None for _ in range(len(self.dim_shape))]]

Starred expressions in subscripts only parse on Python 3.11+. NeMo declares
requires-python = ">=3.10" (with a Programming Language :: Python :: 3.10
classifier and black/isort 3.10 targets), so on Python 3.10 importing the module
raised SyntaxError: invalid syntax, which breaks cache-aware streaming inference
(e.g. examples/asr/asr_cache_aware_streaming/speech_to_text_cache_aware_streaming_infer.py).

The index tuple is now constructed explicitly:

shifted_indices = shifted_indices[(..., *(None for _ in range(len(self.dim_shape))))]

This uses standard tuple iterable-unpacking (valid since Python 3.5), is semantically
identical to the original indexing, and parses on every supported interpreter.

Fixes #15797

Collection: [ASR]

Changelog

• Build the trailing-axis index tuple explicitly in DynamicLengthTensor.append_no_checks_
  so it no longer relies on Python 3.11+ starred-subscript syntax.

Usage

Cache-aware streaming inference now imports and runs on Python 3.10:

from nemo.collections.asr.parts.utils.streaming_utils import CacheAwareStreamingAudioBuffer

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Additional Information

Verification performed locally:

• Confirmed the original line raises SyntaxError on CPython 3.10; the new line compiles.
• python -m py_compile passes for the full file on CPython 3.10.
• Confirmed the expression compiles on CPython 3.10, 3.11, 3.12, 3.13, 3.14, and 3.15.0b3.
• Verified indexing equivalence with the original for dim_shape lengths 0-3.
• black, isort, flake8 (.flake8.speech), and pylint (.pylintrc.speech, 10.00/10) all pass.

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[gauravbyte]

Hi @nithinraok, could you please review this small fix when you get a chance?

Summary: It resolves #15797 — nemo/collections/asr/parts/utils/streaming_utils.py used a PEP 646 starred expression directly inside a subscript (x[..., *[None for _ in ...]]), which only parses on Python 3.11+. Since NeMo declares requires-python = ">=3.10", importing the module raised SyntaxError on 3.10 and broke cache-aware streaming inference.

Fix: build the index tuple explicitly — x[(..., *(None for _ in ...))] — which uses standard tuple unpacking (valid since 3.5), is semantically identical, and parses on CPython 3.10–3.15. It's a 1-line change (+3/-1).

Verification: confirmed the old line raises SyntaxError on 3.10 and the new line compiles on 3.10–3.15; py_compile passes for the full file on 3.10; verified indexing equivalence for dim_shape lengths 0–3; black, isort, flake8 (.flake8.speech), and pylint (.pylintrc.speech, 10.00/10) all pass locally. DCO check is green.

Since this is a community fork PR, the NVIDIA-runner CI is gated — could a maintainer kick it off with /ok to test when convenient? Thanks!

[gauravbyte]

Hi @nithinraok would you be able to review this when you have a moment?

What it fixes (#15797): On Python 3.10, importing streaming_utils.py fails with SyntaxError because it used a PEP 646 starred expression inside a subscript (x[..., *[None for _ in ...]]), which only parses on 3.11+. NeMo declares requires-python = ">=3.10", so this breaks cache-aware streaming inference on 3.10.

The change: build the index tuple explicitly — x[(..., *(None for _ in ...))] — which is standard tuple unpacking, semantically identical, and works on CPython 3.10–3.15. One-line change.

Verified locally: old line raises SyntaxError on 3.10; new line compiles on 3.10–3.15; indexing matches the original.

This is a community fork PR, so NVIDIA-runner CI is gated —could a maintainer trigger /ok to test when convenient? Thanks!

[nithinraok]

/ok to test 66e3b2f

[nithinraok]

@KunalDhawan can you help review and verify this change.

[nithinraok]

Thanks for the PR @gauravbyte

[KunalDhawan]

Thanks for the PR and for fixing this, @gauravbyte! This correctly resolves the Python 3.10 SyntaxError from the PEP 646 starred-subscript (which only parses on 3.11+) that was breaking cache-aware streaming import, and the explicit-tuple form is semantically identical. LGTM!