Application

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Application#

import traitlets
from traitlets.config import Application
Application._instance = None

Command line#

The core feature of the Application class is that it behaves like traitlets.config.Config, but it can override class properties from the command line arguments. You just jave to pass arguments like <class name>.<attribute>=<value> when calling the prograr, just in the configuration script for the traitlets.config.Config.

The following cell defines pythhon script that defines the inheritor of the Application, that has the parameter trait in it - consider how to set the value of parameter.

%%writefile /tmp/my_application.py
import traitlets
from traitlets.config import Application
from traitlets.utils import cast_unicode

class MyApplication(Application):
    parameter = traitlets.Unicode(
        default_value="default",
        config=True
    )

if __name__ == "__main__":
    MyApplication.launch_instance()
    my_application = MyApplication.instance()
    print(my_application.parameter)

Writing /tmp/my_application.py

The following cell calls the previously created scriptip without any additional arguments.

!python3 /tmp/my_application.py

default

As a result, the MyApplication.instance().parameter will have a default value. The following cell runs the same script, but passes the value as a CLI argument.

!python3 /tmp/my_application.py --MyApplication.parameter="new value"

new value

Sometimes it usefull to intialise Application from python code. You can do this by passing argumets as a list[str] to the initialize method.

import os
os.chdir("/tmp")
from my_application import MyApplication

app = MyApplication()
app.initialize(["--MyApplication.parameter", "new value"])
app.parameter

'new value'
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