.. _managing_environments:

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Managing python virtual environments
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It is always recommended to use a virtual environment while developing Python applications.
They essentially allow you to create a “virtual” isolated Python installation and install packages into that virtual installation.
When you switch projects, you can simply create a new virtual environment and not have to worry about breaking the packages installed in the other environments.

Create a new environment with Conda
===================================

One method to create a Python virtual environment is through the Conda package manager.
Conda is an open-source package management system and environment management system.
With conda, you can create, export, list, remove, and update environments that have different versions of Python and/or packages installed in them.
Switching or moving between environments is called activating the environment.

.. warning::

  Ensure that Anaconda or Miniconda is installed on your OPH Cluster.
  Check if you can loaded the module (module load anaconda3/xx);
  otherwise, you may need to install it in the cluster
  (visit the  `Anaconda website <https://www.anaconda.com/download>`_)


Once you load a version of anaconda, you can create and manage Python environments using the conda command.
To create an environment, use the following conda command:

.. code::

  conda create --name my_env python=3.9

This will create a conda environment named whatever value you put in place for [my_env], using Python version 3.9.
This Python version can be modified to a specific version of Python that you want your environment to use.

You have also the option to create a Conda environment from a YAML file by executing the following command:

.. code::

  conda env create --file envname.yml

where the YAML file lists all the packages and their versions that you want to include in your Conda environment.
Here's an illustrative example:

.. code-block:: BASH

  name: my_env
  channels:
    - defaults
  dependencies:
    - python=3.8
    - numpy=1.19.2
    - pandas=1.1.3

This method ensures consistent package versions across different environments and makes it easier to reproduce the environment on different systems.

Activiating the Environment
===========================

After creating an environment, you need to activate it before use.
You can activate it using the following command:

.. code::

  conda activate my_env

Once your environment is activated, you will see your command line prompt change:

.. code::

  (my_env)[username@ophfe2 ~]$

It will start with your environment name in parenthesis at the start of the prompt.


Installing Packages Inside An Environment
=========================================

Once inside your environment, you can install additional packages with the **conda install** command.
Some packages must be installed from a specific channel, such as conda-forge.
To install a package from a specific channel, such as conda-forge, use the command:

.. code::

  conda install -c conda-forge PACKAGE

You can also install a specific version of a package by using the command:

.. code::

  conda install PACKAGE=VERSION