Display Modules

Urwid’s display modules provide a layer of abstraction for drawing to the screen and reading user input. The display module you choose will depend on how you plan to use Urwid.

../_images/display_modules.png

Typically you will select a display module by passing it to your MainLoop constructor, eg:

loop = MainLoop(widget, ..., screen=urwid.curses_display.Screen())

If you don’t specify a display module, the default main loop will use raw_display.Screen by default

# These are the same
loop = MainLoop(widget, ...)
loop = MainLoop(widget, ..., screen=urwid.raw_display.Screen())

Raw and Curses Display Modules

Urwid has two display modules for displaying to terminals or the console.

The raw_display.Screen module is a pure-python display module with no external dependencies. It sends and interprets terminal escape sequences directly. This is the default display module used by MainLoop.

The curses_display.Screen module uses the curses or ncurses library provided by the operating system. The library does some optimization of screen updates and uses termcap to adjust to the user’s terminal.

The (n)curses library will disable colors if it detects a monochrome terminal, so a separate set of attributes should be given for monochrome mode when registering a palette with curses_display.Screen High colors will not be used by the curses_display.Screen module. See Setting a Palette below.

This table summarizes the differences between the two modules:

raw_display curses_display
optimized C code no YES
compatible with any terminal no YES [1]
UTF-8 support YES YES [2]
bright foreground without bold YES [3] no
88- or 256-color support YES no
mouse dragging support YES no
external event loop support YES no
[1]if the termcap entry exists and TERM environment variable is set correctly
[2]if python is linked against the wide version of ncurses
[3]when using xterm or gnome-terminal

Other Display Modules

CGI Web Display Module web_display

The urwid.web_display module lets you run your application as a CGI script under Apache instead of running it in a terminal.

This module is a proof of concept. There are security and responsiveness issues that need to be resolved before this module is recommended for production use.

The tour.py and calc.py example programs demonstrate use of this module.

Screenshot Display Module html_fragment

Screenshots of Urwid interfaces can be rendered in plain HTML. The html_fragment.HtmlGenerator display module lets you do this by simulating user input and capturing the screen as fragments of HTML each time html_fragment.HtmlGenerator.draw_screen() is called.

These fragments may be included in HTML documents. They will be rendered properly by any browser that uses a monospaced font for text that appears in <pre> tags. HTML screenshots have text that is searchable and selectable in a web browser, and they will shrink and grow when a user changes their browser’s text size.

The example screenshots are generated with this display module.

LCD Display Module lcd_display

Almost any device that displays characters in a grid can be used as a screen. The lcd_display module has some base classes for simple LCD character display devices and a complete implementation of a lcd_display.CF635Screen for Crystal Fontz 635 USB displays with 6 buttons.

The lcd_cf635.py example program demonstrates use of this module.

Setting a Palette

The MainLoop constructor takes a palette parameter that it passes to the register_palette() method of your display module.

A palette is a list of display attribute names and foreground and background settings. Display modules may be run in monochrome, normal or high color modes and you can set different foregrounds and backgrounds for each mode as part of your palette. eg:

loop = MainLoop(widget, palette=[
    ('headings', 'white,underline', 'black', 'bold,underline'), # bold text in monochrome mode
    ('body_text', 'dark cyan', 'light gray'),
    ('buttons', 'yellow', 'dark green', 'standout'),
    ('section_text', 'body_text'), # alias to body_text
    ])

The Display Attributes section of this manual describes all the options available.

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