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- Add Python3 and venv to the README - Add a section on how to set up a host if the python command is not available. Update #4037
138 lines
3.9 KiB
ReStructuredText
138 lines
3.9 KiB
ReStructuredText
.. SPDX-License-Identifier: CC-BY-SA-4.0
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.. Copyright (C) 2020 Chris Johns <chrisj@rtems.org>
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.. _host-os:
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Python
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======
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RTEMS uses Python in a range of host tools for users and
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developer. RTEMS supports:
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#. Python3 and Python2 for user tools,
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#. Python3 for developer tools.
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Python2 is now **end of life** however the RTEMS Project will continue to
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provide support for its user commands. We do this to support older host
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operating systems some users may be forced to use. At some point the
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project will drop support for Python2 so we recommend users look at ways to
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transition to Python3 if it is not easily available.
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Developers of RTEMS are required to have Python3 available. RTEMS tools used
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by developers for the development and maintenance of RTEMS are Python3 only.
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All RTEMS Tools that can be invoked from the command line start with the
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following line:
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.. code-block::
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#! /usr/bin/env python
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The ``env`` command is available on all POSIX host operating systems and it
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searches the ``$PATH`` environment variable for the ``python`` command invoking
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it with the script as the first argument. This means you need to have a
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suitable ``python`` command on your host to run the RTEMS user tools. Not all
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hosts provide a ``python`` command. If your host does not you need to find a
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way to provide one. The following are some examples you can use to solve this
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problem.
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Python2 by default always provides a ``python`` command.
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Virtual Environment
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~~~~~~~~~~~~~~~~~~~
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Python3 provides virtual environment support. This is a great way to manage
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Python on a single host. You can have a number of virtual environments with a
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different mix of installed Python packages with different versions that do not
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clash.
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Virtual environment always provide a ``python`` command. This makes it ideal
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if your host only provides Python3 and there is no default ``python`` command.
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A virtual environment is created once and when you need to use it you activate
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it and when finished you deactivate it.
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The following shows how to create a virtual environment using different
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methods. You can select the method that best suites you.
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To create a virtual environment using the Python3 ``venv`` module:
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.. code-block:: none
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python3 -m venv rtems-py
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To create a virtual environment for a specific version of Python3 you
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can enter the command:
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.. code-block:: none
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python3.7 -m venv rtems-py
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You can also install the ``virtualenv`` package on your host if it is
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avaliable then enter the following create command:
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.. code-block:: none
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virtualenv rtems-py
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To activate the virtual environment:
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.. code-block:: none
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. rtems-py/bin/activate
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You will see your prompt change to reflect the virtual environment you
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have active. To check if you now have a ``python`` command enter:
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.. code-block:: none
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type python
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The output will be something similar to the following:
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.. code-block:: none
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(rtems-py) $ type python
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python is /home/chris/development/rtems-py/bin/python
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Symbolic Link
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~~~~~~~~~~~~~
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If your host does not provide the ``python`` command you can add a symbolic
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link to it.
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.. note::
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We recommend you do not add the symbolic link in any of your operating
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system controlled directories as it is changing your operating system.
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We suggest you add the symbolic link to a directory under your home directory
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adding that directory to your environment's ``PATH`` variable. The following
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commands show how to do this:
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.. code-block:: none
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cd
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mkdir bin
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cd bin
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ln -s `command -v python3` python
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export PATH=$HOME/bin:$PATH
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.. note::
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You will need to modify your shell's initialization scripts to make the
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``PATH`` change permanent.
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Directly Invoking Python
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~~~~~~~~~~~~~~~~~~~~~~~~
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It is valid to specifically invoke any python script directly. To do this
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simply prepend the specific version of python you wish to use. For example to
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run the ``waf`` build system command with Python3 use:
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.. code-block:: none
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python3 ./waf
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