4.1. Python#
RTEMS uses Python in a range of host tools for users and developer. RTEMS supports:
Python3 and Python2 for user tools,
Python3 for developer tools.
Python2 is now end of life however the RTEMS Project will continue to provide support for its user commands. We do this to support older host operating systems some users may be forced to use. At some point the project will drop support for Python2 so we recommend users look at ways to transition to Python3 if it is not easily available.
Developers of RTEMS are required to have Python3 available. RTEMS tools used by developers for the development and maintenance of RTEMS are Python3 only.
All RTEMS Tools that can be invoked from the command line start with the following line:
#! /usr/bin/env python
The env command is available on all POSIX host operating systems and it
searches the $PATH environment variable for the python command invoking
it with the script as the first argument. This means you need to have a
suitable python command on your host to run the RTEMS user tools. Not all
hosts provide a python command. If your host does not you need to find a
way to provide one. The following are some examples you can use to solve this
problem.
Python2 by default always provides a python command.
4.1.1. Virtual Environment#
Python3 provides virtual environment support. This is a great way to manage Python on a single host. You can have a number of virtual environments with a different mix of installed Python packages with different versions that do not clash.
Virtual environment always provide a python command. This makes it ideal
if your host only provides Python3 and there is no default python command.
A virtual environment is created once and when you need to use it you activate it and when finished you deactivate it.
The following shows how to create a virtual environment using different methods. You can select the method that best suites you.
To create a virtual environment using the Python3 venv module:
python3 -m venv rtems-py
To create a virtual environment for a specific version of Python3 you can enter the command:
python3.7 -m venv rtems-py
You can also install the virtualenv package on your host if it is
avaliable then enter the following create command:
virtualenv rtems-py
To activate the virtual environment:
. rtems-py/bin/activate
You will see your prompt change to reflect the virtual environment you
have active. To check if you now have a python command enter:
type python
The output will be something similar to the following:
(rtems-py) $ type python
python is /home/chris/development/rtems-py/bin/python
4.1.2. Symbolic Link#
If your host does not provide the python command you can add a symbolic
link to it.
Note
We recommend you do not add the symbolic link in any of your operating system controlled directories as it is changing your operating system.
We suggest you add the symbolic link to a directory under your home directory
adding that directory to your environment’s PATH variable. The following
commands show how to do this:
cd
mkdir bin
cd bin
ln -s `command -v python3` python
export PATH=$HOME/bin:$PATH
Note
You will need to modify your shell’s initialization scripts to make the
PATH change permanent.
4.1.3. Directly Invoking Python#
It is valid to specifically invoke any python script directly. To do this
simply prepend the specific version of python you wish to use. For example to
run the waf build system command with Python3 use:
python3 ./waf