CUDA_VISIBLE_DEVICE is of no use

19

It’s also possible to run into this with bad conda environments.

For me

import os
os.environ["CUDA_VISIBLE_DEVICES"] = "2" # just use one GPU on big machine
import torch
assert torch.cuda.device_count() == 1

Failed, but it was because my environment was problematic, and only

import torch 
print(torch.cuda.current_device())

actually raised an error.