A route handler or simply handler is a function that binds to a certain route. The following is a handler called hello_world, and it binds to a /hello.

@app.route('/hello')
async def hello_world(**server):
    yield b'Hello'
    yield b'World!'

or alternative version:

@app.route('/hello')
async def hello_world(response=None, **server):
    await response.write(b'Hello')
    await response.write(b'World!')

    # optional. FYI, it is required on middleware
    response.close()

Each handler is required to accept a keyword arguments in this case **server. Although the name does not have to be server, for example **kwargs.

server is a dict object, which contains other objects that are often needed, such as server['request'] which is an HTTPRequest object, and server['response'] which is an HTTPResponse object.

Before the **server, you can provide some options to fine tune the handler such as chunked, rate, buffer_size, etc.

@app.route('/hello')
async def hello_world(chunked=False, rate=2097152, buffer_size=32768, **server):
    yield b'Hello'
    yield b'World!'

• chunked=False will disable chunked HTTP responses, the default is automatically adjusted for clients.
• rate 2MiB/s is the download speed limit for each client. This is useful for limiting bandwidth usage as well as mitigating bandwidth hogs.
• buffer_size Tremolo will always process data every chunk based on this size.

In addition to the options above, you can define arbitrary options, and they will magically become available in server['context'].options.

@app.route('/hello')
async def hello_world(a=1, rate=2097152, buffer_size=32768, **server):
    print(server['context'].options)

    yield b'Hello'
    yield b'World!'