Lona Scripts

For microservices or small prototypes Lona apps can be run using a single python script.

$ pip install lona

from datetime import datetime

from lona.html import HTML, H1, Div
from lona import LonaApp, LonaView

app = LonaApp(__file__)


@app.route('/')
class ClockView(LonaView):
    def handle_request(self, request):
        timestamp = Div()

        html = HTML(
            H1('Clock'),
            timestamp,
        )

        while True:
            timestamp.set_text(str(datetime.now()))

            self.show(html)

            self.sleep(1)


if __name__ == '__main__':
    app.run()

Command Line Arguments

Note

--syslog-priorities and syslog_priorities were added in 1.8.3

LonaApp.run() supports command line arguments, like Lona Server, to make calls like python your-script.py --port=8081 work.

Option Description
-l / --log-level Set log level to [debug,info,warn,error,critical]
--loggers Enable or disable a given list of loggers
To include a logger use "+{LOGGER_NAME}", to exclude "_{LOGGER_NAME}"
--debug-mode Enable debug log for {messages,views,input-events,view-events}
--syslog-priorities Adds syslog priorities to log [no,auto,always] (auto is default)
--shell Embed a shell in the same process as the server
--shell-server Starts rlpython shell server containing a Lona shell
More Information: Lona Shell
-o Set setting to value before settings.py got loaded
example "-o MY_FEATURE=True"
-O Set setting to value after settings.py got loaded
example "-o MY_FEATURE=True"

LonaApp.run() Arguments

Name Default Description
host 'localhost' (Str) Host to bind against
port 8080 (Int) Port to bind against
log_level 'info' (Str) Set log level to [debug,info,warn,error,critical]
loggers [] (List) Enable or disable a given list of loggers
To include a logger use "+{LOGGER_NAME}",
to exclude "_{LOGGER_NAME}"
debug_mode '' (Str) Enable debug log for {messages,views,input-events}
syslog_priorities 'auto' (Str) Adds syslog priorities to log [no,auto,always]
shutdown_timeout 0 (Int) aiohttp server shutdown timeout
shell False (Bool) Embed a shell in the same process as the server
shell_server_url '' (Str) Lona Shell Server URL
More information: Lona Shell

Settings

A Lona settings object is available in LonaApp.settings.

More Information: Settings

from lona import LonaApp

app = LonaApp(__file__)

app.settings.MAX_WORKER_THREADS = 10

Adding Views

Views can be added by using the LonaApp.route() decorator or by setting LonaApp.routes to a list of lona.routing.Route objects directly.

LonaApp.route() takes the same arguments like lona.routing.Route.

More information: Views

from lona import LonaApp, LonaView
from lona.html import H1

app = LonaApp(__file__)


@app.route('/')
class MyLonaView(LonaView):
    def handle_request(self, request):
        return H1('Hello World')


if __name__ == '__main__':
    app.run()

Setting The Frontend View

The frontend view can be set by using LonaApp.settings.FRONTEND_VIEW or by using the LonaApp.frontend_view() decorator.

More information: Writing A Custom Frontend

from lona import LonaApp, LonaView

app = LonaApp(__file__)


@app.frontend_view
class MyFrontendView(LonaView):
    def handle_request(self, request):
        return {
            'template': self.server.settings.FRONTEND_TEMPLATE,
        }

Adding Middlewares

Middlewares can be added by using the LonaApp.middleware() decorator or by setting LonaApp.settings.MIDDLEWARES to a list of middleware classes or import strings.

More information: Middlewares

from lona import LonaApp

app = LonaApp(__file__)


@app.middleware
class MyMiddleware:
    def handle_request(self, data):
        print('>>', data)

        return data

Adding Templates

Templates can be added by adding template directory paths to LonaApp.settings.TEMPLATE_DIRS or by using the LonaApp.add_template() method.

All paths, besides paths starting with /, have to be relative to the python script.

More information on extending the frontend template: Custom Templates

from lona import LonaApp

app = LonaApp(__file__)

app.add_template('lona/header.html', """
    <h1>My Lona Project</h1.>
""")

app.add_template('lona/header.html', path='lona/header.html')

Adding Static Files

Static files can be added by adding static directory paths to LonaApp.settings.STATIC_DIRS or by using the LonaApp.add_static_file() method.

All paths, besides paths starting with /, have to be relative to the python script.

The default frontend template includes lona/style.css which can be overridden.

from lona import LonaApp

app = LonaApp(__file__)

app.add_static_file('lona/style.css', """
    body {
        background-color: white;
    }
""")

app.add_static_file('lona/style.css', path='lona/style.css')

Custom Error Views

Note

Added in 1.8.3

Custom error views can be set using the decorators LonaApp.error_403_view, LonaApp.error_404_view and LonaApp.error_500_view.

More information on error views: Error Views

from lona import LonaApp, LonaView

app = LonaApp(__file__)


@app.error_403_view
class Error403View(LonaView):
    def handle_request(self, request, exception):
        return '403: Forbidden'


@app.error_404_view
class Error404View(LonaView):
    def handle_request(self, request):
        return '404: Not Found'


@app.error_500_view
class Error500View(LonaView):
    def handle_request(self, request, exception):
        return '500: Internal Error'


if __name__ == '__main__':
    app.run()