virtualenv.md

 # Python Virtual Environments
 
-TO DO
+Python Virtual Environments (or virtualenvs) are a mechanism to install Python packages not available system-wide, in user directories. They also allow you to have a different Python environment for each project, which is useful for example when you need different versions of the same package for different projects.
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+
+A complete guide on virtualenvs can be found [here](https://thepythonguru.com/python-virtualenv-guide/). Next, we report only some basic commands.
+
+
+Create a Python3 virtualenv in the folder `./pyenv` (done once per project):
+```
+python3 -m venv --system-site-packages ./pyenv
+```
+
+Activate the virtualenv (done for each new shell from where you want to execute code belonging to the project):
+```
+source ./pyenv/bin/activate
+```
+
+Deactivate the virtualenv (the `deactivate` command is created when you activate your environment):
+```
+deactivate
+```
+
+After activating a virtualenv, you can install new packages without special permissions using `pip` (guide [here](https://packaging.python.org/tutorials/installing-packages/#installing-from-pypi)). Those packages will be only available within that virtualenv.
+