README.md

Flask to FastAPI Migration Example

This example demonstrates how to use Codegen to automatically migrate a Flask application to FastAPI. For a complete walkthrough, check out our tutorial.

What This Example Does

The migration script handles four key transformations:

1. Updates Imports and Initialization

   # From:
   from flask import Flask
   
   app = Flask(__name__)
   
   # To:
   from fastapi import FastAPI
   
   app = FastAPI()

2. Converts Route Decorators

   # From:
   @app.route("/users", methods=["POST"])
   
   # To:
   @app.post("/users")

3. Sets Up Static File Handling

   # Adds:
   from fastapi.staticfiles import StaticFiles
   
   app.mount("/static", StaticFiles(directory="static"), name="static")

4. Updates Template Rendering

   # From:
   return render_template("users.html", users=users)
   
   # To:
   return Jinja2Templates(directory="templates").TemplateResponse("users.html", context={"users": users}, request=request)

Running the Example

# Install Codegen
pip install codegen

# Run the migration
python run.py

The script will process all Python files in the repo-before directory and apply the transformations in the correct order.

Understanding the Code

• run.py - The migration script
• input_repo/ - Sample Flask application to migrate

Learn More

• Full Tutorial
• Flask Documentation
• FastAPI Documentation
• Codegen Documentation