Create a conda virtual environment

Step 1: install conda

First, make sure conda is installed on your computer. For instance, conda installation on MacOS can be found here.

By default, a conda base environment is activated every time you open a new terminal. You can turn off this auto-activation:

conda config --set auto_activate_base false

Step 2: create an enviroment

Let's create a conda virual environment called myenv. You can also assign which python version would be used in myenv:

åconda create --name myenv
conda create --name myenv python=python3.7

More advanced is installing packages like scipy and seaborn along with creating the environment:

conda create --name myenv scipy seaborn

Now myenv should be shown when you list all conda environments:

conda info --envs

Step 3: always activate the enviroment

You should activate the environment everytime when you are about to use it:

conda activate myenv

Install or remove packages in a conda environment

After activating myenv, you might also want to check what packages you have installed in it:

conda list

You can simply install or uninstall a package like scipy (which is available via conda install) or beautifulsoup4 (which is not available via conda install but can be obtained from Anaconda.org) in myenv:

conda install scipy
conda install -c anaconda beautifulsoup4

Non-conda packages, for instance, lmfit, can be installed via conda-forge:

conda install -c conda-forge lmfit

Removing a package is easy:

conda remove scipy

Use a conda environment in a Jupyter notebook

To use a conda environment in Jupyter notebook, never forget activating this environment before you are installing anything or running any notebook. A new line should always start with the environment name in your terminal, like this...

(myenv)foo@foo:   # type your command here...

At the first-time use, you need to install ipython specifically in this environment myenv via two commands:

conda install -c anaconda ipykernel
python -m ipykernel install --user --name=myenv

Now you are ready to go! Launch the Jupyter notebook, and you should already find myenv listed in the kernel option!

Bonus

If you are also a fan of Jupyter notebook diverse extensions supporting table of contents, spell check, etc., you can install notebook extensions in this environment:

conda install -c conda-forge jupyter_contrib_nbextensions

For example, activate a function toc2 which help automatically generating a table of contents:

jupyter nbextension enable toc2/main

Use a created conda environment in Pycharm

In biref, you can use an existing environment via Pycharm settings:

1. Click Settings/Preferences and choose Project Python Interpreter.
2. Add a project interpreter and select Conda Environment.
3. Choose Existing environment and specify a path to the Conda executable in your file system, for example, \Users\foo\anaconda3\python.exe

More detailed steps can be found in Pycharm documentation.