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torch.cat/concat/concatenate: support dim=None (flatten before concat)#182204

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senekis316:fix/cat-dim-none
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torch.cat/concat/concatenate: support dim=None (flatten before concat)#182204
senekis316 wants to merge 1 commit intopytorch:mainfrom
senekis316:fix/cat-dim-none

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@senekis316 senekis316 commented May 2, 2026

Fixes #70925

Summary

The Python Array API Standard specifies that concat(tensors, dim=None)
should first flatten all tensors then concatenate them, consistent with
numpy.concatenate(axis=None).

Previously, torch.cat([t1, t2], dim=None) raised a RuntimeError.
After this PR:

t1 = torch.tensor([[1, 2], [3, 4]])
t2 = torch.tensor([[5, 6]])
torch.cat([t1, t2], dim=None)
# tensor([1, 2, 3, 4, 5, 6])

Changes
torch/functional.py: Added Python wrapper for cat with dim=None support; concat and concatenate now point to the same wrapper
torch/_refs/__init__.py: Updated _refs.cat (FakeTensor path) with the same logic
common_methods_invocations.py: Added test cases for dim=None

@senekis316
torch.cat/concat/concatenate: support dim=None by flattening tensors …
bc25f0e 
…first

Implements the Python Array API Standard behavior where dim=None causes
all input tensors to be flattened before concatenation, consistent with
numpy.concatenate(axis=None).

Fixes pytorch#70925
@senekis316 senekis316 requested a review from mruberry as a code owner May 2, 2026 04:24
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pytorch-bot Bot commented May 2, 2026

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/182204

Note: Links to docs will display an error until the docs builds have been completed.

This comment was automatically generated by Dr. CI and updates every 15 minutes.

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pytorch-bot Bot commented May 2, 2026

This PR needs a release notes: label

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@drisspg drisspg added the triaged This issue has been looked at a team member, and triaged and prioritized into an appropriate module label May 5, 2026
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allow dim=None in concat

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