dev_deps

Dev Dependencies Example

This example demonstrates how to conditionally include development-only dependencies (debuggers, test runners, linters, etc.) in a Python binary's build graph using PEP 735 dependency groups, a Bazel string_flag, and select().

The Problem

In a typical Python project you have packages needed at runtime (Flask, SQLAlchemy, …) and packages only useful during development (ipdb, pytest, coverage, …). You want both importable when iterating locally, but you don't want them present in a production container image.

How It Works

1. Dependency groups in pyproject.toml (PEP 735)

[project]
dependencies = ["build", "setuptools"]

[dependency-groups]
prod = ["flask"]
dev  = [
    {include-group = "prod"},
    "ipdb",
    "pytest",
]

The dev group composes prod (the runtime deps) with dev-only tools using PEP 735's include-group syntax. uv lock resolves all groups into a single lockfile.

2. Venv selection via .bazelrc

# Default: dev venv, includes ipdb/pytest
common --@pypi//dep_group=dev

# Release config: prod venv only, enable stamping
common:release --@pypi//dep_group=prod
common:release --//:mode=prod
common:release --stamp

The --@pypi//dep_group= flag controls which dependency group the hub makes available. The default is dev (everything importable). --config=release switches to prod (runtime deps only).

3. A string_flag to control dep inclusion

string_flag(
    name = "mode",
    build_setting_default = "dev",
    values = ["dev", "prod"],
)

config_setting(name = "is_dev",  flag_values = {":mode": "dev"})
config_setting(name = "is_prod", flag_values = {":mode": "prod"})

4. A thin wrapper macro

def py_dev_binary(name, deps = [], dev_deps = [], **kwargs):
    py_binary(
        name = name,
        deps = deps + select({
            "//:is_prod": [],
            "//conditions:default": dev_deps,
        }),
        **kwargs
    )

In dev mode (the default), dev_deps are included. In prod mode the select() resolves to an empty list.

5. Using it

py_dev_binary(
    name = "app",
    srcs = ["app.py"],
    main = "app.py",
    deps = ["@pypi//flask"],
    dev_deps = [
        "@pypi//ipdb",
        "@pypi//pytest",
    ],
)

Running the example

cd examples/dev_deps

# Dev mode (default) — ipdb/pytest are available:
bazel run //:app

# Release mode — ipdb/pytest are excluded:
bazel run //:app --config=release

Two coordinated mechanisms

The venv flag and the mode flag work together:

.bazelrc config	--@pypi//dep_group=	--//:mode=	Effect
(default)	dev	dev	Hub exposes all packages; select() includes dev_deps
--config=release	prod	prod	Hub exposes only prod packages; select() excludes dev_deps

The venv flag controls which packages the hub makes available (which wheels are fetched and linked). The mode flag controls which packages the target actually depends on via select(). Both must agree — the .bazelrc configs keep them in sync.