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Create a conda environment as described here:
conda activate <your_conda_env>
conda install ipykernel
Or:
python3 -m pip install ipykernel
python3 -m ipykernel install --user --name <KERNELNAME> --display-name "<DISPLAY NAME>"
Make sure, that python3 is called from the environment
Create my own Apptainer/Singularity container
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