The `pyproject.toml` file is the new standard for declaring Python projects, and it tells a story. Evidence for its significance is the [`tomllib`](https://docs.python.org/3/library/tomllib.html) built-in module introduced in Python 3.11. Many Python tools and linters adopted it as their primary configuration source. You should also use it - whether you publish a library, build an application or even write scripts/notebooks.This talk will take us through the story of modern Python build systems and package managers. We'll learn where they come into play in the development life-cycle, their benefits, and their limitations.Specifically, we will mention:* Hatch* Poetry* PDM* FlitWe will cover dependency resolution and locking with `.lock` files and how to utilize them for reproducible environments and CI environment caches, facilitating development across large teams.We will migrate together a Python project from the legacy `setup.py` file with many additional files into a single `pyproject.toml` with Poetry.