My system is ubuntu 18.04. I have a pre-installed version 3 and 2 of python.
which python3
/usr/bin/python3
python3 -V
Python 3.6.9
which python
/usr/bin/python
python -V
Python 2.7.17
I need to create several virtual environments, one for python 2.7.15 and another for 2.6. how can I do that?
There are different ways of creating virtual python environments. Three popular ones are
I personally like conda a lot.
Assuming you have pip installed, you get virtualenv with
pip install virtualenv
Once installed, you can change into a directory of your choice and create a virtual environment like this
virtualenv myenvironmentname
If you want to use a different python version in your virtual environment, you can specify this with the --python flag.
virtualenv --python=/usr/bin/python2.6 myenvironmentname
However, please note that this requires you to have the python version you specify installed in advance, virtualenv will not take care of that for you (have a look at Use different Python version with virtualenv for more details). So you'll need local installations of the versions you desire.
You then can activate the environment with
myenvironmentname/bin/activate
and go ahead to use pip to install packages, etc. Have a look at
pip freeze --help
to find out on how to make your environment reusable.
pipenv combines pip and virtualenv.
You can install it using
pip install --user pipenv
Pipenv takes care of dependencies on a project basis
cd myprojectfolder
pipenv install
This will create a Pipfile which will track dependencies and a virtualenv (see https://docs.python-guide.org/dev/virtualenvs/ for more details).
To create an environment using a specific version, you can do
pipenv install --python '/usr/bin/python2.6'
or
pipenv install --python 2.6
Cmp. Set python version when creating virtualenv using pipenv. If you also have pyenv installed, the second form will prompt pipenv to attempt to install non-existing versions, afaik.
Anaconda Python is a python distribution (with a focus on data science) that comes with its own package and virtual environment manager named conda. Anaconda Python is not available in the official package repository of Ubuntu 18.04 LTS but needs to be installed in another way (the official documentation can be found here: https://docs.anaconda.com/anaconda/install/linux/).
To create an environment with conda, do
conda create --name myenvironmentname python=2.7.15
In contrast to virtualenv, the environments are by default not created in the present working directory, but installed into the envs directory in your conda directory. conda will also take care to install the proper python version, that is at least as long as it is part of the default channel (see below).
You can then activate said environment with
conda activate myenvironmentname
As I wrote above, the python version you specify needs to be available from the configured conda channels. python2.6 however, was removed from the default channel. To remedy this, you can add the free channel back to your default list (see https://docs.conda.io/projects/conda/en/latest/user-guide/configuration/free-channel.html for more details):
conda config --set restore_free_channel true
After that you can
conda create --name myotherenvironmentname python=2.6
And switch between the environments as you like
conda activate myotherenvironmentname
For python3 python -m venv <your_virtual_enviroment_path> for python2 virtualenv <your_virutal_enviroment_path>
The to activate source <your_virtual_environment_path>/bin/activate. And to deactivate deactivate. Finally to check what is activated echo $VIRTUAL_ENV
I strongly recommend for one virtual environment for each project.
