Python protocol

Each component can use Python script to extend it’s own functionality. Python script is not limited and can use any modules or server resources providing rich backend event-driven operations.

Local context

Python code declares component local context with variables’ and methods names’ accessible inside any component expression or script. There are some helper variables are predefined:

  • ctx - dictionary of all local variables, introduced to perform reactive writing:

    message: str = "..."

def action_reactive(node):
    ctx['message'] = "Clicked!"

def action_silent(node):
    global message
    message = "Clicked!"

  • refs - dictionary of named references

  • session - current session::Session instance:

    session.log("read me in the console")

  • _ - language translation function:

    message = _("Hello, {}", user_name)

  • logger - server-side prepared logger

All variables above are predefined, but to avoid IDE checker errors, pantra provides special “dummy” module with variables definition pantra.ctx:

from pantra.ctx import *

message: Property[str] = ""

def action(node):
    # all variables are imported from `ctx` to suppress error messages
    ctx["message"] = _("hello")
    refs["title"].set_text("foo")
    session.log("bar")
    logger.info("here")

All local variables are exposed to override by component usage, however, there is also exposed variables explicit annotation convention via Property meta-class:

message: Property[str] = "Hello there!"

Events

pantra introduces event-driven model, what means each user interaction perform event, which can run server-side action.

Reserved actions:

  • def init(): - initialize component context before rendering. Basically this method returns nothing, but when False value is returned - ContextInitFailed exception raised preventing component creation.

  • def on_render(): - executes after component rendering to perform final changes

  • def on_restart(): - executes before very first rendering

  • def node_processor(node): - executes after attributes evaluation before rendering for each node. This method makes possible to use custom attributes and tags. Just note possible running slowdown, because of calling thi method on each node.

  • action.on_kill - executes when task is killed by scheduler:

    def long_running_action(node):
    do_smth_long()

def long_task_stopped():
    ctx["message"].set_text("Eventually stopped")

long_running_action.on_kill = long_task_stopped