.. index:: Python
.. _Python:

Python
======

Description
-----------

Python is a widely used high-level programming language for general-purpose programming.

User instructions
-----------------

Python version 2.7.13 is installed on all workstations from the repository and is the default version you get by simply typing ``python``. Version 3.5.3 is also installed from the repositories and this version can be executed by typing ``python3``.

To make python package modules available you should first load the module corresponding to the version of python it was compiled with. For example

.. code-block:: bash

    $ module load python/3.5.3

Will make a number of python packages compiled with python3 available. The majority of python packages have been made available both as python2 and python3 versions.

Additionally, we have a full SciPy stack with the latest version of python and many packages installed as a single module and compiled with Intel compilers and MKL libraries as the :ref:`CMTH SciPy Stack`.

Virtual Environments
--------------------

Virtual environments allow you to create a directory of python packages associated with a particular python version, over which you have full control.

From python3.5 on, virtual environments can be created and activated without any additional software by eg:

.. code-block:: bash

    $ mkdir my_env
    $ python3 -m venv my_env
    $ . my_env/bin/activate

You'll notice a change in your prompt to indicate the environment is active. To deactivate it, use the ``deactivate`` command.

While active, the ``python`` command will point to whichever version of python you used to create the environment. And using e.g. ``pip install numpy`` will install the latest version of numpy to your environment, and make it available to any python code you run. I suggest keeping any virtual environments on workspace as they can easily exceed several hundred megabytes in size once a handful of packages are installed.

Source
------

http://www.python.org

License
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PSF License (Python Software Foundation). From version 2.2 on this is GPL compatible.

Admin notes
-----------

We just have the python versions from the Debian repositories currently.

The python modules don't load any binaries or libraries, they simply make different sets of compiled modules available.