how to reuse global site-packages in conda env

In case anyone is coming back to this now, for conda 4.7.12, entering export PYTHONNOUSERSITE=True before the conda activate call successfully isolated the conda environment from global/user site packages for me.

On the other hand, entering export PYTHONNOUSERSITE=0 allows the conda environment to be reintroduced to the global/user site packages.

Note: This is instead of the previously suggested export PYTHONNOUSERSITE=1.

you cannot do this explicitly in conda, where the principle is that envs are entirely separate.

but the current default behavior of conda is to allow all global user site-packages to be seen from within environments, as mentioned in this question. so, the default behavior will allow you to do as you wish, but there is no way to allow only "some specific" global packages as requested.

this behavior has caused one or two issues. to avoid it, export PYTHONNOUSERSITE=1 before source activate <your env>. note that the devs are planning to change the default behavior to set PYTHONNOUSERSITE=1 in 4.4.0 (per the second issue linked).