PEP-517 introduced changes not in Python itself but rather in its ecosystem. The idea is pretty simple: let's store configs for all tools in
pyproject.toml file, in
tool.TOOL_NAME section. For example, for mypy:
[tool.mypy] files = ["my_project"] python_version = 3.8
At this moment, almost all popular tools support
pyproject.toml as the configuration file, in one way or another: mypy, pytest, coverage, isort, bandit, tox, etc. The only exception from the tooling I use is flake8.
pyproject.toml, many tools used to use
setup.cfg for the same purpose, but this format (INI) has a few disadvantages comparing to TOML: it's not well-standartized, and the only type supported type of values is string.