whydep 0.1.3

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

# Look up a single package
wd certifi
whydep certifi        # same tool, longer alias

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

# Scan all direct dependencies for unused ones
wd --find-deprecated

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)

If no imports are found for a direct dependency, it is marked as removable:

Why is 'flask' installed?

· (not directly imported — may be aliased or dynamically imported)
(can be removed)

└── (project root)

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

--find-deprecated

Scans all direct dependencies and lists those with no imports found in your source files:

Unused direct dependencies (2):

  certifi — no imports found, can be removed
  idna    — no imports found, can be removed

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.