Extensions for URWID
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README.md

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|    |   /|       _/\   \/\/   /   ||    |  \ |    __)_ 
|    |  / |    |   \ \        /|   ||    `   \|        \
|______/  |____|_  /  \__/\  / |___/_______  /_______  /
                 \/        \/              \/        \/ 

Introduction

URWID is a powerful library that allows you to write command-line interfaces in the Python language. While URWID is very powerful, it is quite low-level compared to existing UI toolkits, which can make development of more advanced user interface a bit difficult.

The main idea behind URWIDE is to extend URWID with a domain-specific language to describe console-based interfaces, drastically reducing the amount of code required to create console-based applications.

URWIDE's declarative, text-based UI description language supports:

  • MVC-like architecture
  • Custom stylesheets
  • Event handling (key, focus, press, edit)
  • I18N (string collections)

To give you an idea of what URWIDE can provide, here is a very simple helloworld.py example:

import urwide

# This is the equivalent of a CSS stylesheet
CONSOLE_STYLE = """
Frame         : Dg,  _, SO
header        : WH, DC, BO
"""

# This is the description of the actual interface
CONSOLE_UI = """\
Hdr URWIDE Hello world
___

Txt Hello World !                     args:#txt_hello
GFl
Btn [Hello !]                         &press=hello
Btn [Bye   !]                         &press=bye
End
"""

# This is the handling code, providing the logic
class Handler(urwide.Handler):
    def onHello( self, button ):
        self.ui.widgets.txt_hello.set_text("You said hello !")
    def onBye( self, button ):
        self.ui.end("bye !")

# We create a console application 
urwide.Console().create(CONSOLE_STYLE, CONSOLE_UI, Handler()).main()

UI Description Language

URWIDE allows to describe a user interface using a very simple line-oriented language. You can define a complete UI in just a few lines. This description allows you to:

  • Identify your widgets with a unique name
  • Associate detailed information and tooltip
  • Bind style information to your widgets
  • Bind event handlers

The description syntax is very simple, and simply consists of a set of lines of the following form:

CLS DATA? [ID|STYLE|INFO|EVENT]* [ARGUMENTS]

as an example, here is the definition of a button with Click me! as label, which will be available as btn_click, displayed using the clickButton style, displaying the CLICK tooltip when focused, and calling the clicked callback when pressed :

Btn [Click me!] #btn_click @clickButton !CLICK &press=clicked

To sum up the available attributes:

  • CLS is a three letter code that corresponds to the widget code

  • DATA is a widget-specific text content

  • ID sets the identifier of the widget

  • STYLE sets the style class of the widget

  • EVENT defines an event handler attached to the widget

  • INFO defines the widget tooltip and detailed information

  • ARGUMENTS defines additional widget attributes

  • Widget identifier

    #id
    
  • Widget style class

    @style
    
  • Widget tooltip

    !TEXT
    
  • Widget info

    ?TEXT
    
  • Event handling

    &event=method
    

    Supported events:

      - `focus`
      - `edit`
      - `key`
    
  • Python arguments

    name=value, name=value, name=value
    
  • Comments

    # This is a comment
    

    Comments are useful to annotate your URWIDE source code, or to enable/disable parts of it. Comments are simply lines starting with the # character.

Blocks

Ple
Txt I am within the above pile
End

or

GFl
Txt Here are buttons
Btn [previous]
Btn [next]
End
SYNTAX DESCRIPTION
#name Widget name, makes it accessible as ui.widgets.name
@class Style class associated with the widget.
&event=callback Makes the onCallback method of the ui.handler() react to the event (press, key, edit, focus) when it occurs on the widget.
!TOOLTIP ui.strings.TOOLTIP or "TOOLTIP" is used as a tooltip for the widget (when it is focused)
?INFO ui.strings.INFO or "INFO" is used as information for the widget (when it is focused) arg=value, ... Additional Python arguments that will be passed to the widget constructor (eg. multiline=true for Edit)
# comment a comment line that will be ignored when parsing

Supported Widgets

URWIDE tries to support most used URWID widgets, and also introduces pseudo widgets that facilitate the specification of your application layout.

Blank

EOL

A blank widget is simply an empty line within the UI description.

Divider

---
===
:::

These three forms create dividers composed of respectively -, = and : characters. In case you will want a particular pattern in your divider, you can user the following form:

Dvd ~-~-

Which will make you a divider composed of ~-~-.

Text

Txt TEXT
Txt TEXT args:ARGUMENTS

Examples

Txt Hello, I'm a text 
Txt Hello, I'm a text args:align='left'

Note _________________________________________________________________ Be sure to use the args: prefix to give arguments to the text, because otherwise your arguments will be interpreted as being part of the displayed text.

Button

Btn [LABEL]

Choice

Chc [ :group] I am an unselected option
Chc [X:group] I am a selected option
Chc [X:other] I am a selected option from the 'other' group
Chc [ :group] I am an unselected option args:#my_choice

A choice is composed of:

  • Its state and group represented by the leading '[S:GROUP]', where 'S' is either ' ' or 'X' and 'GROUP' is any string. Groups are availabled in as 'ui.groups.GROUP' ('ui.groups' is a 'UI.Collection' instance)

  • Its label, following the state and group definition. It can be free-form text.

  • The ui arguments, optionally following the label, but prefixed by 'args:'

Pile

Ple
...
End

Gridflow

Gfl 
...
End

Box

Box border=1
...
End

Boxes allow to draw a border around a widget. You can simply indicate the size of the border using the border attribute.

Columns

Col
    ***
End

Summary

CODE WIDGET TYPE
Txt Text widget
Edt Edit widget
Btn Button widget
Chc RadioButton widget
Dvd Divider widget
Ple Pile container
GFl GridFlow container
Box Box (not in URWID) container

Event handling

URWIDE provides support for handling events and binding event handlers to each individual widget. The events currently supported are:

  • focus (any), which is triggered when the widget received focus
  • key (any), which is triggered when a key is pressed on a widget
  • edit (Edit), which is triggered after an Edit was edited
  • press (Buttons, CheckBox), which is triggered when a button is pressed

Events are handled by handlers, which are objects that define methods that implement a particular reaction. For instance, if you have an event named showHelp, you handler class will be like that:

class MyHandler(urwide.Handler):

    def onShowHelp( self, widget ):
        # Do something here

And then, if you want to trigger the "showHelp" event when a button is pressed:

Btn [Show help] &press=showHelp

This will automatically make the binding between the ui and the handler, provided that you register your handler into the ui:

ui.handler(MyHandler())

Collections

URWIDE will create an instance of the urwide.UI class when given a style (will be presented later) and a UI description. This instance will take care of everything for you, from events to widgets. You will generally only want to access or modify the widgets and strings collections.

Both collections can be edited by accessing values as attribute. Setting an attribute will add a key within the collection, accessing it will return the bound value, or raise an exception if the value was not found.

ui.strings.SOME_TEXT = "This text can be used as a value in a widget"

ui.widgets

Style syntax

[STYLE] : FG, BG, FN
  • STYLE is the name of the style
  • FG is the foreground color
  • BG is the backgrond color
  • FN is the font style

A style name can be:

  • URWID widget name (Edit, Text, etc)
  • style name (defined by @style in the widgets list)
  • widget id, as defined by the #id of the UI

Focus styles can be specified by appending * to each style name:

Edit        : BL, _, SO
Edit*       : DM, Lg, SO

means that all Edit widgets will have black as color when unfocused, and dark magenta when focused.

Here is a table that sums up the possible values that can be used to describe the styles. These values are described in the URWID reference for the Screen class.

CODE VALUE FOREGROUND BACKGROUND FONT
WH white yes no -
BL black no yes -
YL yellow yes no -
BR brown yes no -
DR dark red no yes -
DB dark blue yes yes -
DG dark green yes yes -
DM dark magenta yes yes -
DC dark cyan yes yes -
Dg dark gray yes no -
LR light red yes no -
LG light green yes no -
LB light blue yes no -
LM light magenta yes no -
LC light cyan yes no -
Lg light gray yes yes -
BO bold - - yes
UL underline - - yes
SO standout - - yes
_ default yes yes yes

Using dialogs:

    dialog = Dialog()
    # Don't know why this is necessary, but it doesn't work if it's not there
    sialog.handler(dialog_handler)
    self.pushHandler(dialog_handler)

    def dialog_end():
        self.popHandler()