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How to write a module

Introduction

Adding a new module to bumblebee-status is straight-forward:

  • Add a new Python module in bumblebee_status/modules/contrib/. The name of the module will be the name that the user needs to specify when invoking bumblebee-status (i.e. a module called bumblebee_status/modules/contrib/test.py will be loaded using bumblebee-status -m test)
  • Alternatively, you can put your module in ~/.config/bumblebee-status/modules/
  • The module name must follow the Python Naming Conventions
  • See below for how to actually write the module
  • Test (run bumblebee-status in the CLI)
  • Make sure your changes don’t break anything: ./coverage.sh
  • If you want to do me a favour, run your module through black -t py34 before submitting

Pull requests

The project gladly accepts PRs for bugfixes, new functionality, new modules, etc. When you feel comfortable with what you’ve developed, please just open a PR. Somebody will look at it eventually :) Thanks!

Coding guidelines

I’m pretty open to whatever style you use, but if it’s all the same to you (and yes, I know that the current codebase is only slowly adapting to this): - Please favour double quotes for strings. For private methods/variables, please use a leading __ (e.g. __output rather than _output)

For anything else, please run your code through black.

Hello world

This example will show “hello world” in the status bar:

"""Short description in RST format

   please have a look at other modules, this will go into the
   documentation verbatim (list of modules)
"""

import core.module
import core.widget

class Module(core.module.Module):
    def __init__(self, config):
        super().__init__(config, core.widget.Widget(self.full_text))

    def full_text(self, widgets):
        return 'hello world'

# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4

Of modules and widgets

There are two important concepts for module writers: - A module is something that offers a single set of coherent functionality - A module has 1 to n “widgets”, which translates to individual blocks in the i3bar.

Very often, this is a 1:1 relationship, and a single module has a single widget. If that’s the case for you, you can stop reading now :)

Otherwise, you have a number of ways to handle widgets: - During the super().init__(...) inside the module’s constructor, you can specify a list of widgets, and those will comprise the widgets (in ordered fashion) - During runtime, you can set a new list of widgets by using the self.add_widget() method of the module to add new widgets and self.clear_widgets() method to remove all widgets.

Adding widgets at runtime

If you want to add widgets during runtime, please use the add_widget() method of the module:

def do_something(self):
    self.add_widget(full_text="my sample text", name="<optional name>")

TODO: expand on this

Periodic updates (update() vs. full_text)

bumblebee-status modules have two different ways to update their data: 1. Each interval, the callback registered when the widget was created is called. You can do arbitrarily complex things there 2. Each interval, before the widget’s callback is invoked, a generic update(self, widgets) method is called on the module

Largely, where you want to put your update code is up to you. My observations: - If you want to change the widgets a module has, you have to stick with update() - For simple modules, doing the data update in the widget callback is simplest (see kernel, for example)

Widget states

Each widget inside a module can have a list of states (for example, two predefined states are warning and critical). States define how a widget is rendered (i.e. which fields in the theme file are selected to draw it.

Somewhat paradoxically, to give a widget a state, a method called def state(self, widget) has to be defined on the module. The reason for this is that the module typically contains all of the statefulness, so assumedly, it's easier to determine the state of a widget from the module, rather than from the widget itself.

The state() method simply returns a list of strings, which make up the state this particular widget has.

The themeing code then iterates these states and selects the matching theme information from the theme file. This, it does by performing a "best match" search through the theme, like this:

  • Is there a theme definition for the module that in turn contains a JSON object for the state? If so, use that (for example: "cpu": { "critical": { "fg": "#ff0000" } })
  • If not, is there a theme definition inside the defaults or cycle theme entries?

For more details on that, please refer to How to write a theme

If multiple states match on the "same level", the last state in the state list is used. For example, if a module returns [ "critical", "warning" ] as state, typically, the widget will be drawn as warning.

One important helper method is def threshold_state(value, warning, critical), which each module possesses. Using that, it is very easy to define warning and critical states when the widget represents a simple numeric value.

Sounds confusing? An example will clarify: Let's say your widget returns a percentage (disk usage, or CPU usage). The widget should be marked as "warning" when the percentage is above 50, and as "critical", if it is above 90. This, you would do like this:

def state(self, widget):
    return self.threshold_state(self.__value, 50, 90)

Advanced topics

Event handlers

The core.input module can be used to execute callbacks during mouse events:

import core.module
import core.widget
import core.input

class Module(core.module.Module):
    @core.decorators.every(minutes=60, seconds=20)
    def __init__(self, config):
        super().__init__(config=config, widgets=<widgets>)

        core.input.register(widget, button=core.input.LEFT_MOUSE, cmd=<cmd>)

The command can be either a CLI tool that will be directly executed (e.g. cmd='shutdown -h now') or a method that will be executed. The method’s signature needs to be: def <name>(self, event), where “event” is the event data provided by i3wm.

The full list of possible bindings: - LEFT_MOUSE - RIGHT_MOUSE - MIDDLE_MOUSE - WHEEL_UP - WHEEL_UP

Setting a default update interval

To change the default update interval, you can use a simple decorator:

import core.module
import core.widget
import core.decorators

class Module(core.module.Module):
    @core.decorators.every(minutes=60, seconds=20)
    def __init__(self, config):
        super().__init__(config=config, widgets=<widgets>)

NOTE: This makes the update interval of the module independent of what the user configures via -i <interval>! It is still possible to override the module’s interval using -p <module>.interval=<value>, however.

Redraw outside the update interval

Sometimes, it is desirable to redraw a widget dynamically, even outside its update interva. This can be useful if the value to be displayed is calculated in a separate thread. In such a scenario, the update() method would simply trigger of a thread and the actual value would be available later (but presumably before the next update call).

If that is the case, it is possible to fire off an event in the thread to cause the affected widget to be redrawn, like this:

import core.event

# later
core.event.trigger("update", [<list of module IDs>], redraw_only=True)

A concrete example of this can be found in the module redshift, and a couple of others.

Scrolling content

If a widgets produces a large amount of content, it might be desirable to limit the amount of space the widget can occupy and scroll the content, if necessary.

This behaviour can be achieved using the scrollable decorator like this:

import core.module
import core.widget
import core.decorators

class Module(core.module.Module):
    def __init__(self, config, theme):
        super().__init__(config, theme, core.widget.Widget(self.description))

@core.decorators.scrollable
def description(self, widget):
    pass # TODO: implement

There are a couple of parameters that can be set on the affected module, either in the module using self.set() or via the CLI using the --parameter flag:

  • scrolling.width: Integer, defaults to 30, determines the minimum width of the widgets, if makewide is specified
  • scrolling.makewide: Boolean, defaults to true, determines whether the widgets should be expanded to their minwidth scrolling.bounce: Boolean, defaults to true, determines whether the content should change directions when a scroll is completed, or just marquee through