whydep 0.1.1

Show why a Python package is installed by tracing its lock file dependency graph

whydep

A fast Rust CLI that answers "why is this Python package installed?" by tracing your project's lock file dependency graph and showing which source files use it.

Install

pip install whydep
# or
uv add --dev whydep

Usage

# Run from your project directory
wd certifi
whydep certifi        # same tool, longer alias

# Point at a different project
wd certifi --dir /path/to/my-project

Example output

For a transitive dependency:

Why is 'MarkupSafe' installed?

└── jinja2
    └── flask
        · src/main.py:1: import flask
        · src/main.py:2: from flask import Flask, request
        └── (project root)

For a direct dependency:

Why is 'flask' installed?

· src/main.py:1: import flask
· src/main.py:2: from flask import Flask, request

└── (project root)

Lines starting with · show where your code imports the direct dependency that pulled the package in.

Supported lock files

Tool	Lock file
uv	uv.lock
Poetry	poetry.lock

uv.lock is preferred when both exist. The lock file is searched in the given directory and up to 3 parent directories.

Configuration

Add a [tool.whydep] section to your pyproject.toml to limit source scanning to specific directories (faster, less noise):

[tool.whydep]
src = "src"              # single directory
# src = ["src", "tests"] # or multiple

Without this setting the entire project directory is scanned.