Python Tutorial (7): Virtual Environment dan Dependency Management

System Python:
  requests==2.25    ← project A butuh ini
  requests==2.31    ← project B butuh ini
  ❌ Konflik!

project-a/.venv → requests==2.25 ✅
project-b/.venv → requests==2.31 ✅

# Buat virtual environment
python3 -m venv .venv
 
# Aktivasi
source .venv/bin/activate       # Linux/macOS
# .venv\Scripts\activate        # Windows
 
# Verifikasi
which python       # .venv/bin/python
python --version
pip --version
 
# Deaktivasi
deactivate

# Install package
pip install requests flask sqlalchemy
 
# Install versi spesifik
pip install "requests>=2.28,<3.0"
pip install "django~=4.2"     # compatible release (4.2.x)
 
# Export dependency
pip freeze > requirements.txt
 
# Install dari file
pip install -r requirements.txt
 
# Upgrade
pip install --upgrade requests
pip install --upgrade pip

# requirements.txt: pin exact versions untuk reproducibility
requests==2.31.0
flask==3.0.0
sqlalchemy==2.0.23
gunicorn==21.2.0

# requirements-dev.txt: development dependencies
-r requirements.txt
pytest==7.4.3
ruff==0.1.8
mypy==1.7.1

pip install pip-tools
 
# requirements.in: deklarasi top-level dependency
# requirements.txt: generated, pinned, resolved

# requirements.in
flask
sqlalchemy
celery

pip-compile requirements.in    # → requirements.txt with hashes
pip-sync requirements.txt      # sync environment exactly

# Install Poetry
curl -sSL https://install.python-poetry.org | python3 -
 
# Buat project baru
poetry new myproject
 
# Atau init di project existing
cd myproject
poetry init
 
# Install dependency
poetry add requests flask
poetry add --group dev pytest ruff
 
# Install semua dari lock file
poetry install
 
# Run di venv Poetry
poetry run python main.py
poetry run pytest
 
# Shell aktivasi
poetry shell

[tool.poetry]
name = "myproject"
version = "0.1.0"
description = "My awesome project"
authors = ["Alice <alice@mail.com>"]
python = "^3.11"
 
[tool.poetry.dependencies]
python = "^3.11"
flask = "^3.0"
sqlalchemy = "^2.0"
pydantic = "^2.5"
 
[tool.poetry.group.dev.dependencies]
pytest = "^7.4"
ruff = "^0.1"
mypy = "^1.7"
 
[build-system]
requires = ["poetry-core"]
build-backend = "poetry.core.masonry.api"

# Install uv
curl -LsSf https://astral.sh/uv/install.sh | sh
 
# Buat project
uv init myproject && cd myproject
 
# Add dependencies
uv add requests flask
uv add --dev pytest ruff
 
# Sync environment
uv sync
 
# Run
uv run python main.py
uv run pytest

[project]
name = "myproject"
version = "0.1.0"
requires-python = ">=3.11"
dependencies = [
    "flask>=3.0",
    "sqlalchemy>=2.0",
]
 
[project.optional-dependencies]
dev = [
    "pytest>=7.4",
    "ruff>=0.1",
]
 
[tool.ruff]
line-length = 100
 
[tool.pytest.ini_options]
testpaths = ["tests"]

myproject/
├── pyproject.toml          # project metadata + dependencies
├── poetry.lock / uv.lock  # lock file (commit!)
├── .python-version         # Python version (pyenv)
├── .gitignore
├── README.md
├── src/
│   └── myproject/
│       ├── __init__.py
│       ├── main.py
│       └── utils.py
├── tests/
│   ├── __init__.py
│   └── test_main.py
└── .venv/                  # JANGAN commit

.venv/
__pycache__/
*.pyc
dist/
*.egg-info/
.env

# Install pyenv
curl https://pyenv.run | bash
 
# Install Python version
pyenv install 3.12.1
pyenv install 3.11.7
 
# Set per-project
cd myproject
pyenv local 3.12.1    # buat .python-version
 
# Global default
pyenv global 3.12.1