Python and Python3

Here is a very brief description why you type python or python3 at the command line.

Backward Compatibility

You need to understand this term to appreciate the issue between the commands python and python3.

To say python version X is fully backward compatible means all python programs written for python versions less than X will work with python version X.

This is not the case between python versions 2 and 3.

Why is Python 3 not Backward Compatible?

There is no lack of information regarding the decision to break backward compatibility with python3. Here are two articles from highly regarded voices in the Python community:

• Python 3 Q & A - Nick Coghlan's Python Notes,
• Why Python 3 exists - Brett Cannon

If you're at the very beginning of learning to program and/or brand new to Python, you might want to simply accept that python 3 is not backward compatible and move on. There's some great details, and history in those articles though, they're interesting for many reasons.

The Good News

Python 3 was initially released in December, 2008, and python 2 support officially ended in January 2020. Unless you're maintaining old Python code, you really don't need to know any details other than you might need to run python3 instead of python.

If you're considering using a module that still doesn't support Python version 3, you're almost certainly asking for extra work.

Why Not Settle on the Command python Now?

Python was around for many hears before version 3 stirred the pot. Thus there are probably millions of lines of Python version 2 code still running in the wild. If a system still has Python version 2 code, scripts running that code will be using the command python. If the python command runs Python version 3, the scripts will most likely fail.

Now, consider needing to update a system that has Python version 2 scripts. It's highly unlikely you can update all those scripts at one time. This puts you in a position to need both python and python3 on the same system. Which also puts you in the position of having the comannd python3 embedded in some of your system scripts.

Now you've completed the migration of your version 2 code to version 3, you can get rid of the python command. However, you still have the python3 command in your system scripts. Thus you need to continue to support python3 as the command to run Python version 3.

Can I Configure python to also run python3?

If you're absolutely sure there is nothing on your system expecting the command python to be Python version 2, you can create an alias, or whatever the configuration is on your system, for python to be Python version 3.

If you system came with Python version 2 already installed as python, you'll almost certainly break something if you globally change python to run version 3.