Python Virtual Environment

Python virtual environment is a method of creating an isolated environment for Python projects. It enables each project to have its own dependencies, regardless of what dependencies every other project has. To read more about Python virtual environments, click here.

Creating a Python Virtual Environment
Load one of the Python modules available on Cheaha in your environment. [ravi89@login001 ~]$ module avail Python

-- /share/apps/rc/modules/all -- Python/2.7.10-goolf-1.7.20      Python/2.7.13-intel-2017a Python/2.7.10-intel-2015b       Python/2.7.3-foss-2016a Python/2.7.11-foss-2016a        Python/2.7.3-goolf-1.7.20 Python/2.7.11-foss-2016b        Python/2.7.5-goolf-1.7.20 Python/2.7.11-goolf-1.7.20      Python/2.7.8-intel-2015b Python/2.7.11-intel-2015b       Python/2.7.9-goolf-1.7.20 Python/2.7.11-intel-2016a       Python/2.7.9-intel-2015b Python/2.7.12-foss-2016a        Python/3.2.3-goolf-1.7.20 Python/2.7.12-foss-2016b        Python/3.5.1-foss-2016a Python/2.7.12-intel-2015b       Python/3.5.1-intel-2016a Python/2.7.12-intel-2016a       Python/3.6.1-intel-2017a Python/2.7.13-GCCcore-6.3.0-bare Python/3.6.3-intel-2017a

Once you have loaded Python, we would use virtualenv to create and manage virtual environments. [ravi89@login001 Python_Environments]$ module load Python/3.6.3-intel-2017a [ravi89@login001 Python_Environments]$ virtualenv test_environment Using base prefix '/share/apps/rc/software/Python/3.6.3-intel-2017a' New python executable in /data/user/ravi89/Python_Environments/test_environment/bin/python Installing setuptools, pip, wheel...done. [ravi89@login001 Python_Environments]$

Activating a Virtual Environment
Once a virtual environment has been created, you need to activate it to be in the virtual environment. [ravi89@login001 Python_Environments]$ source test_environment/bin/activate (test_environment) [ravi89@login001 Python_Environments]$ Activating the virtual environment will change your shell’s prompt to show what virtual environment you’re using, test_environment in the above case, and modify the environment so that you can install Python packages for that particular environment.

Maintaining a Virtual Environment
After this you can install the packages that you would like for this environment, using pip. pip is a package management system used to install and manage software packages written in Python. (test_environment) [ravi89@login001 Python_Environments]$ pip install numpy Collecting numpy Downloading numpy-1.14.0-cp36-cp36m-manylinux1_x86_64.whl (17.2MB) 100% |████████████████████████████████| 17.2MB 77kB/s Installing collected packages: numpy Successfully installed numpy-1.14.0 (test_environment) [ravi89@login001 Python_Environments]$ ls test_environment/lib/python3.6/site-packages/ easy_install.py        pip-9.0.1.dist-info  setuptools-38.4.0.dist-info numpy                  pkg_resources        wheel numpy-1.14.0.dist-info __pycache__          wheel-0.30.0.dist-info pip                    setuptools (test_environment) [ravi89@login001 Python_Environments]$

You can use this method to install a Python application alongside all the dependencies that it requires.

Deactivating a Virtual Environment
After you are done using the virtual environment, you can use deactivate command to go back to your bash shell environemnt. (test_environment) [ravi89@login001 Python_Environments]$ deactivate [ravi89@login001 Python_Environments]$ It would change your shell's prompt and remove the name of the virtual environment that you were in.

Sharing a virtual environment
You can use pip freeze to list all the packages in a virtual environment and copy it to a requirement.txt.file pip freeze > requirements.txt

Now you can create new virtualenv and after activating that virtual environment, install all the packages using the following command. pip install -r requirements.txt