python-doc/Docs/Libs/FastAPI/01-Setup.md

FastAPI – Environment Setup

This document describes the initial setup required to prepare a Python environment for developing a FastAPI application. The steps below ensure isolation, dependency management, and reproducibility across environments.

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Prerequisites

Before starting, ensure the following are installed on your system:

• Python 3.8 or higher
• pip (Python package manager)
• venv module (included by default with most Python installations)

You can verify your Python version with:

python3 --version

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Step 1: Create a Virtual Environment

A virtual environment isolates project dependencies and prevents conflicts with system-wide Python packages.

From the project root directory, run:

python3 -m venv .venv

This command creates a .venv directory containing the isolated Python environment.

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Step 2: Activate the Virtual Environment

Activate the virtual environment before installing any dependencies.

Linux / macOS

source .venv/bin/activate

Windows (PowerShell)

.venv\Scripts\Activate.ps1

After activation, your shell prompt should indicate that the virtual environment is active.

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Step 3: Install FastAPI

With the virtual environment activated, install FastAPI using pip:

pip install fastapi

This installs the FastAPI framework and its required dependencies.

Note: In a real application, FastAPI is commonly used with an ASGI server such as uvicorn, which can be installed later if needed.

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Step 4: Freeze Dependencies

To ensure reproducibility across environments (local, CI/CD, staging, production), export the installed dependencies to a requirements file:

pip freeze > requirement.txt

This file should be committed to version control and used by deployment pipelines to install exact dependency versions.

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Resulting Files

After completing the steps above, your project directory should include:

• .venv/ – Python virtual environment (should not be committed to VCS)
• requirement.txt – Dependency lock file

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Best Practices

• Always activate the virtual environment before working on the project
• Do not commit .venv/ to source control
• Keep requirement.txt updated when adding or upgrading dependencies
• Use the same requirement.txt in CI/CD pipelines for consistent builds

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