PYTHON-VIRTUAL-ENVS.md

pySLAM2 Virtual Environment

The following instructions allow you to create a custom pyslam virtual environment by using the package python3-venv. You will be able to run pyslam scripts within such environment.

Basic Installation

In order to run main_vo.py with venv, get in the root of this repository and run the following command:

$ . pyenv-create.sh 

N.B.: do not forget the dot! (without '/' !)

This will create a custom pyslam environment and will also activate it. Now, from the same terminal, you can run:

$ python3 -O main_vo.py

If you want to use a new terminal, you need to activate the pyslam environment as explained in this section

If you are under macOS, please check this document.

Full Installation

In order to run main_slam.py with venv, get in the root of this repository and run the following command:

$ . install_all_venv.sh  

N.B.: do not forget the dot! (without '/' !)

This will compile the required thirdparty packages and will also activate the created pyslam environment. Now, from the same terminal, you can run:

$ python3 -O main_slam.py

If you want to use a new terminal, you need to activate the pyslam environment as explained in this section

Create a pyslam python virtual environment

You already see this above. In order to create a custom pyslam python virtual environment, get in the root of this repository and run the following command:

$ . pyenv-create.sh 

N.B.: do not forget the dot! (without '/' !)

This will create and activate a python virtual environment pyslam where to safely run pyslam scripts.

Activate the created pyslam environment

Run the following command:

$ . pyenv-activate.sh 

Now, you can launch pySLAM scripts.

Deactivate pyslam environment

Run the command:

$ deactivate 

Delete pyslam environment

To delete the pyslam environment, run

$ . pyenv-delete.sh 

---

General Notes About Python Virtual Environments

Below, you can find some useful details. The scripts mentioned above make the work for you.

Install virtualenv package

sudo apt install python3-venv

Where to create a new virtual environment

You can create a new directory where to deploy the new environment with name venv-name

$ mkdir -p ~/.python/venvs/<venv-name> 
$ cd ~/.python/venvs/<venv-name>

Create a new virtual environment inside the directory:

$ python3 -m venv <venv-name>

Activate the environment

In order to use this environment’s packages/resources in isolation, you need to “activate” it. To do this, just run the following:

$ source ~/.python/venvs/<venv-name>/bin/activate

This will return in your shell a prefixed prompt with the name of your environment

(env) $

This is the indicator that env is currently active, which means the python executable will only use this environment’s packages and settings.

Deactivate the environment

Run the following command

(env) $ deactivate

This will removed the prefixed prompt.

Install packages from requirements.txt

You can generate a requirements.txt file by running:

$ pip3 freeze > requirements-pip3.txt 

You can install from such a file by runnning:

$ pip3 install -r requirements-pip3.txt

N.B.: the file requirements.txt generated by pip3 cannot be used with conda (and viceversa)!

Check if you are in an activated virtual environment

From shell check the shell prefix, as explained above

From a script, you can use the following code:

function get_after_last_slash(){
    ret=$(echo $1 | sed 's:.*/::')
    echo $ret 
}
function get_virtualenv_name(){
    cmd_out=$(printenv | grep VIRTUAL_ENV)
    virtual_env_name=$(get_after_last_slash $cmd_out)
    echo $virtual_env_name
}

the function get_virtualenv_name returns the name of the path of the activated virtual environment. If no virtual environment has been activated then the output will be empty.

Links

• https://realpython.com/python-virtual-environments-a-primer/ (first and clear reference)