Update introyt model tutorial APIs

[Vasanthadithya-mundrathi]

Fixes #3856

Description

Updates the Building Models tutorial to use the current PyTorch API style:

• specifies dim=1 for the TinyModel softmax layer
• replaces Python 2-style super(...) calls with super().__init__()

Verification

• python3 -m py_compile beginner_source/introyt/modelsyt_tutorial.py
• MPLBACKEND=Agg /tmp/docathon-torch-venv/bin/python beginner_source/introyt/modelsyt_tutorial.py

Checklist

• The issue that is being fixed is referred in the description
• Only one issue is addressed in this pull request
• Labels from the issue that this PR is fixing are added to this pull request
• No unnecessary issues are included into this pull request.

cc @subramen

[pytorch-bot]

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[Copilot]

Pull request overview

Updates the Building Models with PyTorch Intro YouTube tutorial code to align with current PyTorch/Python best practices and remove a Softmax deprecation warning, addressing Issue #3856.

Changes:

• Specify the Softmax dimension explicitly in TinyModel via torch.nn.Softmax(dim=1).
• Modernize module initialization by replacing Python 2-style super(Class, self).__init__() with super().__init__() in TinyModel, LeNet, and LSTMTagger.

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[svekars]

@claude

[claude]

Claude finished @svekars's task in 1m 4s —— View job

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Review of PR #3895

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LGTM — this is a clean, minimal fix that addresses exactly what issue #3856 reported.

Changes look correct:

1. torch.nn.Softmax(dim=1) (modelsyt_tutorial.py:56) — Good. Softmax without an explicit dim has been deprecated since PyTorch 1.0 and raises a warning at runtime. dim=1 is correct here since TinyModel expects batch input of shape (batch, 10) from Linear(200, 10).

2. super().__init__() (lines 51, 153, 252) — Straightforward modernization. Python 3-style super() is preferred and equivalent in all single-inheritance cases like these.

3. No other instances of super(ClassName, self) or bare Softmax() remain in the file.

No issues found. The changes are minimal, correct, and well-scoped.

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[Vasanthadithya-mundrathi]

CLA is signed now, and issue #3856 is assigned to me. Could a maintainer add the issue labels (docathon-2026, intro, easy) to this PR and approve the first-time contributor workflows when convenient?