Python Functions in the /api Directory

Vercel supports existing projects that define file-based Python functions in an /api directory. File-based Python functions map .py files to routes and load ASGI applications, WSGI applications, or BaseHTTPRequestHandler subclasses.

For new Python applications, use a framework preset for FastAPI, Flask, or Django. To run a Python backend alongside another framework, use Services.

Without a detected Python framework preset, each .py file inside /api becomes a separate Vercel Function. Vercel serves each function at its file path. For example, api/index.py serves /api, and api/users.py serves /api/users.

Each .py file must define one of these top-level names:

• app for an ASGI or WSGI application
• application for a WSGI application
• handler for a class that inherits from BaseHTTPRequestHandler

The following function uses BaseHTTPRequestHandler:

from http.server import BaseHTTPRequestHandler
 
class handler(BaseHTTPRequestHandler):
 
    def do_GET(self):
        self.send_response(200)
        self.send_header('Content-Type', 'text/plain')
        self.end_headers()
        self.wfile.write('Hello, world!'.encode('utf-8'))

A Python framework preset takes precedence over file-based functions. When Vercel detects a framework preset, the framework application handles all requests, and files under /api don't become separate Vercel Functions.

Use the functions property in vercel.json to configure file-based Python functions. For example, use excludeFiles to exclude files that the functions don't need at runtime:

{
  "$schema": "https://openapi.vercel.sh/vercel.json",
  "functions": {
    "api/**/*.py": {
      "excludeFiles": "{tests/**,__tests__/**,**/*.test.py,**/test_*.py,fixtures/**,__fixtures__/**,testdata/**,sample-data/**,static/**,assets/**}"
    }
  }
}

For dependency files, Python versions, streaming, bundle size limits, and file system behavior, see the Python runtime reference.

• Deploy a FastAPI app on Vercel
• Deploy a Flask app on Vercel
• Deploy a Django app on Vercel
• Combine frontends and backends with Services