Modern Python Tooling — Part 2: pyproject.toml, Ecosystem, and Python Version Highlights¶

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This part covers the modern config file (pyproject.toml), the old-to-new toolchain mapping, and quality-of-life improvements in recent Python releases.

pyproject.toml — the modern config file¶

Modern Python projects use pyproject.toml instead of setup.py, setup.cfg, and separate config files:

[project]
name = "my-project"
version = "0.1.0"
requires-python = ">=3.11"
dependencies = [
    "requests>=2.31",
    "flask>=3.0",
]

[tool.ruff]
line-length = 88

[tool.pytest.ini_options]
testpaths = ["tests"]

One file, all configuration. No more scattered config files.

The modern Python toolchain¶

Old tool	Modern replacement	Why
`pip`	`uv pip`	10-100x faster, better dependency resolution
`python -m venv`	`uv venv`	Faster, bundled with uv
`pyenv`	`uv python`	Manages Python versions
`pip-tools`	`uv lock`	Lockfiles for reproducible installs
`flake8`	`ruff check`	10-100x faster, more rules
`black`	`ruff format`	Same style, faster
`isort`	`ruff check --select I`	Included in ruff
`setup.py`	`pyproject.toml`	Standard, declarative

You do not need to adopt everything at once. Start with uv for package management, add ruff for linting, and switch to pyproject.toml when you create your own packages.

Python 3.11-3.14 highlights¶

Recent Python releases have brought significant quality-of-life improvements.

Better error messages (3.11+)¶

Python 3.11 points directly to the exact expression that caused an error:

Traceback (most recent call last):
  File "example.py", line 3, in <module>
    result = data["users"][0]["email"]
                               ^^^^^^^
KeyError: 'email'

Before 3.11, you would only get the line number — now Python underlines the exact problematic expression.

`f"{x=}"` debugging (3.8+)¶

Add = inside an f-string to print both the variable name and its value:

x = 42
name = "Alice"
items = [1, 2, 3]

print(f"{x=}")            # x=42
print(f"{name=}")         # name='Alice'
print(f"{len(items)=}")   # len(items)=3

`tomllib` — built-in TOML parser (3.11+)¶

Read pyproject.toml and other TOML files without a third-party library:

import tomllib

with open("pyproject.toml", "rb") as f:
    config = tomllib.load(f)

print(config["project"]["name"])

`StrEnum` (3.11+)¶

Enum members that behave like strings — no need for .value:

from enum import StrEnum

class Color(StrEnum):
    RED = "red"
    BLUE = "blue"

print(Color.RED == "red")    # True
print(f"Color is {Color.RED}")    # "Color is red"

See Enums Explained for more.

`pip audit` — dependency vulnerability scanning¶

Check your installed packages for known security vulnerabilities:

pip install pip-audit
pip audit

New interactive REPL (3.13+)¶

Python 3.13 introduces an improved REPL with: - Multi-line editing with proper indentation - Color-coded output - Paste mode for multi-line code blocks - History search with Ctrl+R

Exception groups and `except*` (3.11+)¶

Handle multiple exceptions raised simultaneously (useful for async code):

try:
    async with asyncio.TaskGroup() as tg:
        tg.create_task(task1())
        tg.create_task(task2())
except* ValueError as eg:
    print(f"Value errors: {eg.exceptions}")
except* TypeError as eg:
    print(f"Type errors: {eg.exceptions}")

Common mistakes¶

Mixing pip and uv in the same environment: Pick one and stick with it. Both write to the same .venv/, so they are compatible, but mixing them can cause confusion about what is installed.

Forgetting to activate the environment:

uv pip install requests    # Installs into .venv, but...
python my_script.py        # ...might use system Python if .venv is not activated!

Always check for (.venv) in your prompt.

Running ruff without saving first: ruff reads files from disk, not your editor buffer. Save before running ruff check.

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