Although the final release of Python 3.13 is scheduled for October 2024, you can download and install a preview version today to explore the new features. Notably, the introduction of free threading and a just-in-time (JIT) compiler are among the most exciting enhancements, both designed to give your code a significant performance boost.
In this tutorial, you’ll:
- Compile a custom Python build from source using Docker
- Disable the Global Interpreter Lock (GIL) in Python
- Enable the Just-In-Time (JIT) compiler for Python code
- Determine the availability of new features at runtime
- Assess the performance improvements in Python 3.13
- Make a C extension module targeting Python’s new ABI
Check out what’s new in the Python changelog for a complete list of the upcoming features and improvements. This document contains a quick summary of the release highlights as well as a detailed breakdown of the planned changes.
To download the sample code and other resources accompanying this tutorial, click the link below:
Get Your Code: Click here to download the free sample code that shows you how to work with the experimental free threading and JIT compiler in Python 3.13.
Take the Quiz: Test your knowledge with our interactive “Python 3.13: Free-Threading and a JIT Compiler” quiz. You’ll receive a score upon completion to help you track your learning progress:
Interactive Quiz
Python 3.13: Free-Threading and a JIT CompilerIn this quiz, you'll test your understanding of the new features in Python 3.13. You'll revisit how to compile a custom Python build, disable the Global Interpreter Lock (GIL), enable the Just-In-Time (JIT) compiler, and more.
Free Threading and JIT in Python 3.13: What’s the Fuss?
Before going any further, it’s important to note that the majority of improvements in Python 3.13 will remain invisible to the average Joe. This includes free threading (PEP 703) and the JIT compiler (PEP 744), which have already sparked a lot of excitement in the Python community.
Keep in mind that they’re both experimental features aimed at power users, who must take extra steps to enable them at Python’s build time. None of the official channels will distribute Python 3.13 with these additional features enabled by default. This is to maintain backward compatibility and to prevent potential glitches, which should be expected.
Note: Don’t try to use Python 3.13 with the experimental features in a production environment! It may cause unexpected problems, and the Python Steering Council reserves the right to remove these features entirely from future Python releases if they prove to be unstable. Treat them as an experiment to gather real-world data.
In this section, you’ll get a birds-eye view of these experimental features so you can set the right expectations. You’ll find detailed explanations on how to enable them and evaluate their impact on Python’s performance in the remainder of this tutorial.
Free Threading Makes the GIL Optional
Free threading is an attempt to remove the Global Interpreter Lock (GIL) from CPython, which has traditionally been the biggest obstacle to achieving thread-based parallelism when performing CPU-bound tasks. In short, the GIL allows only one thread of execution to run at any given time, regardless of how many cores your CPU is equipped with. This prevents Python from leveraging the available computing power effectively.
There have been many attempts in the past to bypass the GIL in Python, each with varying levels of success. You can read about these attempts in the tutorial on bypassing the GIL. While previous attempts were made by third parties, this is the first time that the core Python development team has taken similar steps with the permission of the steering council, even if some reservations remain.
Note: Python 3.12 approached the GIL obstacle from a different angle by allowing the individual subinterpreters to have their independent GILs. This can improve Python’s concurrency by letting you run different tasks in parallel, but without the ability to share data cheaply between them due to isolated memory spaces. In Python 3.13, you’ll be able to combine subinterpreters with free threading.
The removal of the GIL would have significant implications for the Python interpreter itself and especially for the large body of third-party code that relies on it. Because free threading essentially breaks backward compatibility, the long-term plan for its implementation is as follows:
- Experimental: Free threading is introduced as an experimental feature and isn’t a part of the official Python distribution. You must make a custom Python build to disable the GIL.
- Enabled: The GIL becomes optional in the official Python distribution but remains enabled by default to allow for a transition period.
- Disabled: The GIL is disabled by default, but you can still enable it if needed for compatibility reasons.
There are no plans to completely remove the GIL from the official Python distribution at the moment, as that would cause significant disruption to legacy codebases and libraries. Note that the steps outlined above are just a proposal subject to change. Also, free threading may not pan out at all if it makes single-threaded Python run slower than without it.
Until the GIL becomes optional in the official Python distribution, which may take a few more years, the Python development team will maintain two incompatible interpreter versions. The vanilla Python build won’t support free threading, while the special free-threaded flavor will have a slightly different Application Binary Interface (ABI) tagged with the letter “t” for threading.
This means that C extension modules built for stock Python won’t be compatible with the free-threaded version and the other way around. Maintainers of those external modules will be expected to distribute two packages with each release. If you’re one of them, and you use the Python/C API, then you’ll learn how to target CPython’s new ABI in the final section of this tutorial.
JIT Compiles Python to Machine Code
As an interpreted language, Python takes your high-level code and executes it on the fly without the need for prior compilation. This has both pros and cons. Some of the biggest advantages of interpreted languages include better portability across different hardware architectures and a quick development time due to the lack of a compilation step. At the same time, interpretation is much slower than directly executing code native to your machine.
Note: To be more precise, Python interprets bytecode instructions, an intermediate binary representation between pure Python and machine code. The Python interpreter compiles your code to bytecode when you import a module and stores the resulting bytecode in the __pycache__ folder. This doesn’t inherently make your Python scripts run faster, but loading a pre-processed bytecode can indeed speed up their startup time.
Languages like C and C++ leverage Ahead-of-Time (AOT) compilation to translate your high-level code into machine code before you ship your software. The benefit of this is faster execution since the code is already in the computer’s mother tongue. While you no longer need a separate program to interpret the code, you must compile it separately for all target platforms that you want supported. You should also handle platform-specific differences yourself.
