Routing

Map URLs to handler functions using expressive route patterns with typed parameters, wildcards, and regex filters.

Basic Routing

Routes map URL patterns to Python functions. Use the @app.route() decorator to register a handler:

from lcore import Lcore

app = Lcore()

@app.route('/')
def index():
    return 'Welcome home'

@app.route('/about')
def about():
    return 'About page'

Return Types

Handlers can return various types, and Lcore handles them automatically:

Named Routes

@app.route('/users/<id:int>', name='user_detail')
def user_detail(id):
    return {'id': id}

# Build URL from name
url = app.get_url('user_detail', id=42)
# -> '/users/42'

HTTP Methods

By default, routes respond to GET requests. Specify other methods with the method parameter:

@app.route('/items', method='POST')
def create_item():
    return {'created': True}

# Multiple methods on one route
@app.route('/items/<id:int>', method=['GET', 'PUT', 'DELETE'])
def item(id):
    if request.method == 'GET':
        return get_item(id)
    elif request.method == 'PUT':
        return update_item(id)
    elif request.method == 'DELETE':
        return delete_item(id)

Shorthand Decorators

@app.get('/users')
def list_users():
    return {'users': []}

@app.post('/users')
def create_user():
    data = request.json
    return {'id': 1, **data}

@app.put('/users/<id:int>')
def replace_user(id):
    return {'id': id, 'replaced': True}

@app.delete('/users/<id:int>')
def remove_user(id):
    return {'deleted': True}

If a URL matches a route but not the HTTP method, Lcore returns 405 Method Not Allowed with an Allow header listing valid methods.

Dynamic Routes

Capture URL segments as parameters using angle brackets. Parameters are passed as keyword arguments to your handler:

@app.route('/hello/<name>')
def hello(name):
    return f'Hello, {name}!'

# GET /hello/Alice -> "Hello, Alice!"

Typed Parameters

Add a filter to constrain and convert parameter types:

# Integer parameter
@app.route('/users/<id:int>')
def get_user(id):
    return {'id': id, 'type': type(id).__name__}
# GET /users/42 -> {"id": 42, "type": "int"}
# GET /users/abc -> 404

# Float parameter
@app.route('/coords/<lat:float>/<lon:float>')
def location(lat, lon):
    return {'lat': lat, 'lon': lon}

# Path parameter (matches slashes)
@app.route('/files/<filepath:path>')
def serve_file(filepath):
    return static_file(filepath, root='./public')
# GET /files/docs/guide/intro.pdf -> serves the file

# Regex parameter
@app.route('/api/v<version:re:[0-9]+>/status')
def api_status(version):
    return {'api_version': version}

# Multiple parameters
@app.route('/<year:int>/<month:int>/<slug>')
def article(year, month, slug):
    return {'year': year, 'month': month, 'slug': slug}

Async Routes

# No code changes to handlers needed:
app.run(server='gevent', host='0.0.0.0', port=8080)
# or: app.run(server='eventlet', host='0.0.0.0', port=8080)

When async def is acceptable in Lcore

There is one scenario where using async def in Lcore is harmless: calling an async helper that is pure CPU work wrapped in a coroutine with no I/O and no loop-bound state. In practice this is rare. For everything else, prefer sync equivalents.

import asyncio
from lcore import Lcore

app = Lcore()  # Lcore will emit a UserWarning for each async route below

# OK: works, but provides NO concurrency advantage.
# The worker thread is blocked for the duration of the coroutine.
@app.route('/ok-simple')
async def simple():
    # Fine: fast pure-Python computation inside a coroutine.
    return {'result': sum(range(1000))}

# INCORRECT: asyncio.gather() does run both coroutines, but the entire
# gather() blocks the worker thread until both complete. No parallelism.
@app.route('/broken-parallel')
async def broken_parallel():
    # Not concurrent in a WSGI context. Both still run sequentially
    # from the perspective of the OS thread scheduler.
    users, products = await asyncio.gather(fetch_users(), fetch_products())
    return {'users': users, 'products': products}

# INCORRECT: async libraries that require a persistent event loop will
# fail or silently misbehave because each request gets a brand-new loop.
# import httpx
# import asyncpg
# async def broken_db():
#     conn = await asyncpg.connect(...)  # new loop every call, pool unusable
#     ...

# CORRECT: write synchronous handlers.
# Use requests, psycopg2, redis-py, etc.
@app.route('/correct')
def sync_handler():
    # Fast, no overhead, works correctly with every WSGI server.
    return {'type': 'sync'}

Async Middleware

Middleware can also be async:

from lcore import Middleware

class AsyncTimingMiddleware(Middleware):
    name = 'async_timing'
    order = 2

    async def __call__(self, ctx, next_handler):
        import time
        start = time.time()
        result = next_handler(ctx)
        duration = time.time() - start
        ctx.response.set_header('X-Time', f'{duration:.4f}s')
        return result

Route Filters

Create custom route filters for reusable parameter validation and conversion:

# Custom UUID filter
import re

app.add_route_filter(
    'uuid',
    r'[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}',
    to_python=lambda val: val,
    to_url=lambda val: str(val)
)

@app.route('/items/<item_id:uuid>')
def get_item(item_id):
    return {'item_id': item_id}
# GET /items/550e8400-e29b-41d4-a716-446655440000 -> matches
# GET /items/invalid -> 404

The add_route_filter method accepts:

Route Groups

Group routes under a common prefix using the app.group() context manager:

with app.group('/api/v1'):
    @app.route('/users')
    def list_users():
        return {'users': []}

    @app.route('/users/<id:int>')
    def get_user(id):
        return {'id': id}

    @app.route('/products')
    def list_products():
        return {'products': []}

# Routes registered:
#   /api/v1/users
#   /api/v1/users/<id:int>
#   /api/v1/products

Groups can share common configuration:

with app.group('/admin', auth_required=True):
    @app.route('/dashboard')
    def dashboard():
        return 'Admin Dashboard'

Error Routes

Define custom error pages with the @app.error() decorator:

@app.error(404)
def not_found(error):
    return {'error': 'Not found', 'path': request.path}

@app.error(500)
def server_error(error):
    return {'error': 'Internal server error'}

# The error handler receives an HTTPError object with:
#   error.status_code  - HTTP status code
#   error.body         - Error message
#   error.exception    - Original exception (if any)
#   error.traceback    - Traceback string (if debug)

Raising Errors

from lcore import abort, HTTPError

@app.route('/protected')
def protected():
    # Quick abort
    abort(403, 'Access denied')

    # Or raise with more control
    raise HTTPError(
        status=422,
        body='Invalid input',
        headers={'X-Error': 'validation'}
    )

URL Building

Build URLs from route names to avoid hardcoding paths:

@app.route('/users/<id:int>', name='user_detail')
def user_detail(id):
    return {'id': id}

@app.route('/users/<id:int>/posts/<post_id:int>', name='user_post')
def user_post(id, post_id):
    return {'user': id, 'post': post_id}

# Build URLs
app.get_url('user_detail', id=42)
# -> '/users/42'

app.get_url('user_post', id=42, post_id=7)
# -> '/users/42/posts/7'

Route Inspection

List Routes

Use app.show_routes() to get a structured list of all registered routes:

routes = app.show_routes()
for r in routes:
    print(f"{r['method']:6s} {r['rule']:30s} {r['name'] or '-'}")

# GET    /                              index
# GET    /users                         list_users
# POST   /users                         create_user
# GET    /users/<id:int>                user_detail

Each route dict contains: method, rule, name, callback, plugins.

Auto-Generated API Docs

Generate API documentation automatically from your routes, docstrings, and parameter types:

@app.route('/api/users/<id:int>', method='GET', name='get_user')
def get_user(id):
    """Fetch a single user by their unique ID."""
    return {'id': id}

# Get docs as dict
docs = app.api_docs()
print(docs['routes'][0])
# {'method': 'GET', 'rule': '/api/users/<id:int>',
#  'name': 'get_user', 'docstring': 'Fetch a single user...',
#  'parameters': [{'name': 'id', 'type': 'int'}], ...}

# Get docs as JSON string
json_docs = app.api_docs_json()

# Serve docs as an endpoint
@app.route('/docs')
def docs():
    return app.api_docs()