What is the best way to record the Python dependencies for the reproducibility of your projects? What advantages will lock files provide for those projects? This week on the show, we welcome back Python Core Developer Brett Cannon to discuss his journey to bring PEP 751 and the pylock.toml file format to the community.

Brett has been working on a way to move beyond the requirements.txt file for over six years. He was on the show previously to discuss his work on PEP 665, which was rejected. He decided to continue to push forward, authoring PEP 751 last year, which was accepted at the end of March this year.

The PEP calls for a new file format to record your project’s dependencies. The goal was to have a standardized immutable record for what should be installed to reproduce your project in a virtual environment. He discusses working with other packaging projects and the compromises involved in creating a standard.

Course Spotlight: Using the Python subprocess Module

In this video course, you’ll learn how to use Python’s subprocess module to run and control external programs from your scripts. You’ll start with launching basic processes and progress to interacting with them as they execute.

Topics:

00:00:00 – Introduction
00:02:38 – Brett’s roles within the Python community
00:05:41 – How to move beyond requirement.txt?
00:10:58 – What does the community use as project artifacts?
00:15:28 – Building on the success of pyproject.toml
00:17:44 – Introducing PEP 665
00:19:49 – Software Bills of Materials and security
00:25:20 – Back to lock files and security
00:31:08 – Video Course Spotlight
00:32:27 – Not giving up on the idea
00:34:01 – Leading into PEP 751
00:38:54 – Working toward a single multi-platform file
00:43:02 – The final push
00:48:54 – Leaving room for flexibility
00:53:50 – And it’s done, PEP 751 accepted unconditionally
00:58:06 – Keynote speaker at EuroPython 2025
00:58:45 – What are uv workspaces?
01:01:02 – Considering the use of lock files in data science
01:05:23 – Updates about Python for WASI and Emscripten
01:13:51 – Clarification on WASI
01:20:28 – Future conversation about Python launcher
01:23:04 – What are you excited about in the world of Python?
01:24:25 – What do you want to learn next?
01:28:41 – What’s the best way to follow your work online?
01:31:00 – Thanks and goodbye

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