python-venv

CRITICAL RULE

ALWAYS use .venv/bin/python and .venv/bin/pip - NEVER bare python or pip

This ensures you're using the project's virtual environment, not the system Python.

Environment Setup

Create New Environment

# Create venv
python3 -m venv .venv

# Activate (for interactive use)
source .venv/bin/activate

# Or use directly without activating
.venv/bin/python --version

Install Dependencies

# From requirements.txt
.venv/bin/pip install -r requirements.txt

# From pyproject.toml (if using pip)
.venv/bin/pip install -e .

# From pyproject.toml (if using poetry)
poetry install

# Single package
.venv/bin/pip install package-name

Update Dependencies

# Upgrade pip itself
.venv/bin/pip install --upgrade pip

# Upgrade a package
.venv/bin/pip install --upgrade package-name

# Freeze current state
.venv/bin/pip freeze > requirements.txt

Dependency Files

requirements.txt

requests>=2.28.0
pandas==2.0.0
pytest>=7.0.0

pyproject.toml (modern)

[project]
dependencies = [
    "requests>=2.28.0",
    "pandas==2.0.0",
]

[project.optional-dependencies]
dev = ["pytest>=7.0.0", "ruff"]

Troubleshooting

• "Module not found": Check you're using .venv/bin/python
• Permission errors: Don't use sudo with pip in venv
• Conflicting versions: Use pip install --force-reinstall
• Corrupted venv: Delete .venv/ and recreate