ImportError: cannot import name 'ensure_dir_exists'

I want to use jupyter notebook on my virtual environment. After I install nb_conda by running the command "conda install nb_conda", I cannot launch notebook of the virtual environment. The error is:
`ImportError: cannot import name 'ensure_dir_exists'`

I try to update the jupyter_core and jupyter_client by running
`conda update jupyter_core jupyter_client`,
following the suggestion[](https://stackoverflow.com/questions/48372019/importerror-cannot-import-name-ensure-dir-exists). But the error is still there.
I can't figure out why, could someone give a detail explanation about this kind of error?

Reproduce the failure after installing nb_conda in a virtual environment, then inspect the ImportError and the installed jupyter_core and jupyter_client versions. Done means identifying the incompatible dependency or configuration and confirming that the virtual-environment notebook launches successfully.

Written by the indexing model from the issue text.