docs/errors/module_not_found_src_layout.md

ModuleNotFoundError — src/ layout not configured

Date: 2026-04-11
Project: Neural Machine Translation — AI Translator
Environment: Windows 11, Python 3.12.9

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Error message

tests\test_languages.py:5: in <module>
    from ai_translator.languages import (
E   ModuleNotFoundError: No module named 'ai_translator'

Context

Running pytest after confirming pytest was installed. The project uses a src/ layout — all source code lives inside src/ai_translator/ instead of the root.

Why it happened

Python searches the root folder for packages by default. With a src/ layout, the package is one level deeper and Python can't find it without explicit configuration. Additionally, the package was never registered in the environment.

Neural Machine Translation — AI Translator structure

Neural Machine Translation — AI Translator/
├── src/
│   └── ai_translator/      ← Python couldn't find this
│       ├── __init__.py
│       └── languages.py
├── tests/
│   └── test_languages.py
└── pyproject.toml

What fixed it

Step 1 — Created pyproject.toml in the root folder:

[build-system]
requires = ["setuptools>=64"]
build-backend = "setuptools.build_meta"

[project]
name = "ai_translator"
version = "0.1.0"

[tool.setuptools.packages.find]
where = ["src"]

Step 2 — Installed the package in editable mode:

pip install -e .

Lesson learned

The src/ layout requires two things to work:

• pyproject.toml with where = ["src"] so setuptools knows where to look
• pip install -e . to register the package in the active environment

The -e flag means editable — Python points directly to your src/ folder, so code changes are reflected immediately without reinstalling.