Switching torch extra between pypi & torch backend #16368
Description
uv 0.9.4. Consider the following pyproject.toml in an otherwise empty directory:
[project]
name = "moo"
version = "0.1.0"
requires-python = ">=3.13"
dependencies = ["numpy"]
[project.optional-dependencies]
cpu = [
"torch>=2.8.0",
]
cu128 = [
"torch>=2.8.0",
]
pypi = [
"torch>=2.8.0",
]
[tool.uv]
conflicts = [
[
{ extra = "cpu" },
{ extra = "cu128" },
{ extra = "pypi" },
],
]
[tool.uv.sources]
torch = [
{ index = "pytorch-cpu", extra = "cpu" },
{ index = "pytorch-cu128", extra = "cu128" },
{ index = "pytorch-pypi", extra = "pypi" },
]
[[tool.uv.index]]
name = "pytorch-cpu"
url = "https://download.pytorch.org/whl/cpu"
explicit = true
[[tool.uv.index]]
name = "pytorch-cu128"
url = "https://download.pytorch.org/whl/cu128"
explicit = true
[[tool.uv.index]]
name = "pytorch-pypi"
url = "https://pypi.org/simple/"
explicit = trueThis is basically the same as the documented example, with the addition of the pytorch-pypi index as an option.
I've now run the following commands on a machine with a GPU:
$ uv run --extra cpu python -c "import torch; print(torch.cuda.is_available())"
Using CPython 3.13.7
Creating virtual environment at: .venv
Installed 11 packages in 5.26s
False
$ uv run --extra cu128 python -c "import torch; print(torch.cuda.is_available())"
True
$ uv run --extra pypi python -c "import torch; print(torch.cuda.is_available())"
True
$ uv run --extra cpu python -c "import torch; print(torch.cuda.is_available())"
Uninstalled 1 package in 2.45s
Installed 1 package in 3.90s
False
$ uv run --extra pypi python -c "import torch; print(torch.cuda.is_available())"
FalseA little inspection of the verbose logs shows that, when specifying --extra pypi, no package is added or removed. We can look at the syncs to see a bit more explicitly:
$ rm -rf .venv && uv sync --extra pypi
Using CPython 3.13.7
Creating virtual environment at: .venv
Resolved 31 packages in 0.65ms
Installed 27 packages in 4.70s
+ filelock==3.20.0
+ fsspec==2025.9.0
+ jinja2==3.1.6
+ markupsafe==3.0.3
+ mpmath==1.3.0
+ networkx==3.5
+ numpy==2.3.4
+ nvidia-cublas-cu12==12.8.4.1
+ nvidia-cuda-cupti-cu12==12.8.90
+ nvidia-cuda-nvrtc-cu12==12.8.93
+ nvidia-cuda-runtime-cu12==12.8.90
+ nvidia-cudnn-cu12==9.10.2.21
+ nvidia-cufft-cu12==11.3.3.83
+ nvidia-cufile-cu12==1.13.1.3
+ nvidia-curand-cu12==10.3.9.90
+ nvidia-cusolver-cu12==11.7.3.90
+ nvidia-cusparse-cu12==12.5.8.93
+ nvidia-cusparselt-cu12==0.7.1
+ nvidia-nccl-cu12==2.27.5
+ nvidia-nvjitlink-cu12==12.8.93
+ nvidia-nvshmem-cu12==3.3.20
+ nvidia-nvtx-cu12==12.8.90
+ setuptools==80.9.0
+ sympy==1.14.0
+ torch==2.9.0
+ triton==3.5.0
+ typing-extensions==4.15.0
$ uv sync --extra pypi
Resolved 31 packages in 2ms
Audited 27 packages in 13ms
$ uv sync --extra cpu
Resolved 31 packages in 1ms
Uninstalled 17 packages in 3.05s
Installed 1 package in 4.31s
- nvidia-cublas-cu12==12.8.4.1
- nvidia-cuda-cupti-cu12==12.8.90
- nvidia-cuda-nvrtc-cu12==12.8.93
- nvidia-cuda-runtime-cu12==12.8.90
- nvidia-cudnn-cu12==9.10.2.21
- nvidia-cufft-cu12==11.3.3.83
- nvidia-cufile-cu12==1.13.1.3
- nvidia-curand-cu12==10.3.9.90
- nvidia-cusolver-cu12==11.7.3.90
- nvidia-cusparse-cu12==12.5.8.93
- nvidia-cusparselt-cu12==0.7.1
- nvidia-nccl-cu12==2.27.5
- nvidia-nvjitlink-cu12==12.8.93
- nvidia-nvshmem-cu12==3.3.20
- nvidia-nvtx-cu12==12.8.90
- torch==2.9.0
+ torch==2.9.0+cpu
- triton==3.5.0
$ uv sync --extra pypi
Resolved 31 packages in 2ms
Installed 16 packages in 185ms
+ nvidia-cublas-cu12==12.8.4.1
+ nvidia-cuda-cupti-cu12==12.8.90
+ nvidia-cuda-nvrtc-cu12==12.8.93
+ nvidia-cuda-runtime-cu12==12.8.90
+ nvidia-cudnn-cu12==9.10.2.21
+ nvidia-cufft-cu12==11.3.3.83
+ nvidia-cufile-cu12==1.13.1.3
+ nvidia-curand-cu12==10.3.9.90
+ nvidia-cusolver-cu12==11.7.3.90
+ nvidia-cusparse-cu12==12.5.8.93
+ nvidia-cusparselt-cu12==0.7.1
+ nvidia-nccl-cu12==2.27.5
+ nvidia-nvjitlink-cu12==12.8.93
+ nvidia-nvshmem-cu12==3.3.20
+ nvidia-nvtx-cu12==12.8.90
+ triton==3.5.0
$ uv sync --extra cu128
Resolved 31 packages in 2ms
Uninstalled 1 package in 2.75s
Installed 1 package in 4.33s
- torch==2.9.0+cpu
+ torch==2.9.0+cu128
$ uv sync --extra pypi
Resolved 31 packages in 1ms
Audited 27 packages in 4msI presume this is because the torch indices name their wheels e.g. 2.9.0+cpu and 2.9.0+cu128, whereas the pypi wheel is just 2.9.0. But this behaviour did trip us up a bit, so possibly there's some room for improvement here, even if just in the docs.