How to build python 2 (optional)
================================

Note: Tips for building python were taken from this site::

  Tips for building python taken from: https://gist.github.com/lukaslundgren/2659457

Why this may be needed
----------------------

On some Linux systems, e.g. Debian-12, Python 2 is no longer available as 
a package.

The RTEMS source builder that build the RTEMS cross tools however, still depends
on Python 2.

So if your system doesn't have Python 2 installed and there is no package available,
you need to build Python 2 from source with the script "build-python2.sh" that
is described here.

How to build
------------

You first have to review or change some configuration variables in file CONFIG.COMMON.

Activate local Python 2 usage by setting RTEMS_CROSS_USE_LOCAL_PYTHON2 to "yes"
(see :ref:`common configuration variables <common_config_variables>`).

Python 2 directory settings
---------------------------

.. note::
   You usually don't need to change these.

The installation base directory is given on the command line and Python 2 will be
installed in directory "python2" below this.

If you want to fine-tune installation, build and source directories, you can do
this by changing the following variables in file CONFIG.COMMON:

.. _python2_config_variables:

.. note::
  `$INSTALLTOP` is defined by :doc:`bin/setup.sh <setup>`,
  `$TOP` is the directory where rtems-from-scratch is located

+----------------------------+---------------------+------------------------------------------+
| Variable                   | default value       | explanation                              |
+============================+=====================+==========================================+
| PYTHON2_INSTALL_DIR        | $INSTALLTOP/python2 | Directory where Python 2 is installed    |
+----------------------------+---------------------+------------------------------------------+
| PYTHON2_SRC_DIR            | $TOP/src/python2    | Directory where Python 2 sources are put |
+----------------------------+---------------------+------------------------------------------+
| PYTHON2_VERSION            | 2.7.18              | Version of Python 2 that is built        |
+----------------------------+---------------------+------------------------------------------+
| PYTHON2_MAKE_OPTS          | "-s -j"             | Make options for Python 2                |
+----------------------------+---------------------+------------------------------------------+

Prerequisites
-------------

Python 2 needs some libraries and tools to be installed on your system.

For Debian 12 they are listed here:
:ref:`Debian 12 Python 2 prerequisites <debian12_python_prerequisites>`.

Run the build script
--------------------

The python 2 interpreter will be installed in directory PYTHON2_INSTALL_DIR.

Run::

  bin/build-python2.sh

How to use Python 2
-------------------

In file :doc:`CONFIG.COMMON <config_common>` 
variable RTEMS_CROSS_USE_LOCAL_PYTHON2 must be set to "yes".

The Python 2 interpreter is then found by :doc:`build-crosstools.sh <kernel>`
automatically.

If you want to this Python interpreter other applications, source file
`setenv.sh` which is placed in directory $PYTHON2_INSTALL_DIR as it is
defined in file :doc:`CONFIG.COMMON <config_common>`. 

If for example, you defined `INSTALLTOP <setup>` as '/usr/local/rtems' and
didn't change PYTHON2_INSTALL_DIR in file CONFIG.COMMON the command would be::

  . /usr/local/rtems/python2/setenv.sh

This redefines the PATH variable so Python 2 is found. Note that this also
sets LD_LIBRARY_PATH.