Python environment
==================

TPA decides which Python interpreter to use based on the :ref:`distribution it detects <Distribution support>` 
on a target instance. It will use Python 3 wherever possible, and fall
back to Python 2 only when unavoidable.

The ``tpaexec configure`` command will set ``preferred_python_version``
according to the distribution.

.. csv-table::
  :header: Distribution,Python 2,Python 3
  ::widths: 12,12,18
  :align: left
  :class: longtable

  Debian 10/buster,✓,✓ (3.7)
  Debian 9/stretch,✓,✓ (3.5)
  Debian 8/jessie,✓,✗ (3.4)
  Ubuntu 16.04/xenial,✓,✓ (3.5)
  Ubuntu 18.04/bionic,✓,✓ (3.6)
  Ubuntu 20.04/focal,✗,✓ (3.8)
  Ubuntu 22.04/jammy,✗,✓ (3.10)
  RHEL 7.x,✓,✗ (3.6)
  RHEL 8.x,✗,✓ (3.6)

Ubuntu 20.04, 22.04 and RHEL 8.x can be used only with Python 3.

RHEL 7.x ships with Python 3.6, but the librpm bindings for Python 3 are
not available, so TPA must use Python 2 instead. Debian 8 does not have
the Python 3.5+ required to support Ansible.

You can decide for other distributions whether you prefer ``python2`` or
``python3`` , but the default for new clusters is ``python3`` .

Backwards compatibility
-----------------------

For compatibility with existing clusters, the default value of
``preferred_python_version`` is ``python2`` , but you can explicitly
choose ``python3`` even on systems that were already deployed with
``python2`` .

.. code:: yaml

   cluster_vars:
     preferred_python_version: python3

TPA will ignore this setting on distributions where it cannot use Python
3.