# 2.1. Configure Python Environment

This section describes how to configure the Python environment to run experiments and 
develop code for the ETSI TeraFlowSDN controller.
In particular, we use [PyEnv](https://github.com/pyenv/pyenv) to install the appropriate 
version of Python and manage the virtual environments.


## 2.1.1. Upgrade the Ubuntu distribution
Skip this step if you already did it during the creation of the VM.
```bash
sudo apt-get update -y
sudo apt-get dist-upgrade -y
```


## 2.1.2. Install PyEnv dependencies in the VM
```bash
sudo apt-get install -y make build-essential libssl-dev zlib1g-dev libbz2-dev libreadline-dev libsqlite3-dev wget \
    curl llvm git libncursesw5-dev xz-utils tk-dev libxml2-dev libxmlsec1-dev libffi-dev liblzma-dev
```


## 2.1.3. Install PyEnv

We recommend installing PyEnv through  
[PyEnv Installer](https://github.com/pyenv/pyenv-installer).
Below you can find the instructions, but we refer you to the link for updated 
instructions.

```bash
curl https://pyenv.run | bash
# When finished, edit ~/.bash_profile // ~/.profile // ~/.bashrc as the installer proposes.
# In general, it means to append the following lines to ~/.bashrc:
export PYENV_ROOT="$HOME/.pyenv"
command -v pyenv >/dev/null || export PATH="$PYENV_ROOT/bin:$PATH"
eval "$(pyenv init -)"
eval "$(pyenv virtualenv-init -)"
```

In case .bashrc is not linked properly to your profile, you may need to append the 
following line into your local .profile file:

```bash
# Open ~/.profile and append this line:
+source "$HOME"/.bashrc
```


## 2.1.4. Restart the VM
Restart the VM for all the changes to take effect.
```bash
sudo reboot
```


## 2.1.5. Install Python 3.9 over PyEnv

ETSI TeraFlowSDN uses Python 3.9 by default.
You should install the latest update of Python 3.9.
To find the latest version available in PyEnv, you can run the following command:

```bash
pyenv install --list | grep " 3.9"
```

At the time of writing, this command will output the following list:

```
  3.9.0
  3.9-dev
  3.9.1
  3.9.2
  3.9.4
  3.9.5
  3.9.6
  3.9.7
  3.9.8
  3.9.9
  3.9.10
  3.9.11
  3.9.12
  3.9.13
  3.9.14 ** always select the latest version **
```

Therefore, the latest version is Python 3.9.14.
To install this version, you should run:

```bash
pyenv install 3.9.14
    # This command might take some minutes depending on your Internet connection speed 
    # and the performance of your VM.
```


## 2.1.6. Create the Virtual Environment for TeraFlowSDN
The following commands create a virtual environment named as `tfs` using Python 3.9 and 
associate that environment with the current folder, i.e., `~/tfs-ctrl`.
That way, when you are in that folder, the associated virtual environment will be used, 
thus inheriting the Python interpreter, i.e., Python 3.9, and the Python packages 
installed on it.

```bash
cd ~/tfs-ctrl
pyenv virtualenv 3.9.14 tfs
pyenv local 3.9.14/envs/tfs
```

In case that the correct pyenv does not get automatically activated when you change to 
the tfs-ctrl/ folder, then execute the following command:

```bash
cd ~/tfs-ctrl
pyenv activate 3.9.14/envs/tfs
```

After completing these commands, you should see in your prompt that now you're within 
the virtual environment `3.9.14/envs/tfs` on folder `~/tfs-ctrl`:
```
(3.9.14/envs/tfs) tfs@tfs-vm:~/tfs-ctrl$
```


## 2.1.7. Install the basic Python packages within the virtual environment
From within the `3.9.14/envs/tfs` environment on folder `~/tfs-ctrl`, run the following 
commands to install the basic Python packages required to work with TeraFlowSDN.
```bash
cd ~/tfs-ctrl
./install_requirements.sh
```