> For the complete documentation index, see [llms.txt](https://book.konstantinsecurity.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.konstantinsecurity.com/readme/pentest/python-virtualenv.md). # Python virtualenv `virtualenv` is a tool to create isolated Python environments. You can read more about it in the [Virtualenv documentation](https://virtualenv.pypa.io/en/stable/). This article provides a quick summary to help you set up and use a virtual environment. ## A Note About Python 3.6 and Ubuntu 16.04 LTS If you’re running Ubuntu 16.04 LTS (or and earlier version), Python 3.5 is likely installed by default. *Don’t remove it!* To get Python 3.6, follow the instructions in this section. ### Add the PPA Run the following command to add the Python 3.6 PPA. ``` sudo add-apt-repository ppa:jonathonf/python-3.6 ``` ### Check for Updates and Install Check for updates and install Python 3.6 via the following commands. ``` sudo apt-get update sudo apt-get install python3.6 ``` Now you have three Python version, use `python` to run version 2.7, `python3` for version 3.5, and `python3.6` for version 3.6. For more information on this subject, check out Ji m’s article [How to Install Python 3.6.1 in Ubuntu 16.04 LTS](http://ubuntuhandbook.org/index.php/2017/07/install-python-3-6-1-in-ubuntu-16-04-lts/). ## Create a Virtual Python Environment `cd` to your project directory and run `virtualenv` to create the new virtual environment. The following commands will create a new virtual environment under my-project/my-venv. ``` cd my-project virtualenv --python python3.6 venv ``` ## Activate the Environment Now that we have a virtual environment, we need to activate it. ``` source venv/bin/activate ``` After you activate the environment, your command prompt will be modified to reflect the change. ## Add Libraries and Create a *requirements.txt* File After you activate the virtual environment, you can add packages to it using `pip`. You can also create a description of your dependencies using `pip`. The following command creates a file called `requirements.txt` that enumerates the installed packages. ``` pip freeze > requirements.txt ``` This file can then be used by collaborators to update virtual environments using the following command. ``` pip install -r requirements.txt ``` ## Deactivate the Environment To return to normal system settings, use the `deactivate` command. ``` deactivate ``` After you issue this command, you’ll notice that the command prompt returns to normal.