# 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.

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

    loop = MainLoop(widget, ..., screen=urwid.display.curses.Screen())

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

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

## Raw and Curses Display Modules

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

The `display.raw.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 `display.curses.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 `display.curses.Screen` High colors will not be used by the `display.curses.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-/256-/24-bit 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 `display.web`

The `urwid.display.web` 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 `display.html_fragment.HtmlGenerator` display module lets you do this by simulating user input and capturing the screen as fragments of HTML each time `display.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 `display.lcd`

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

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

See also

Urwid on a Crystalfontz 635 LCD

## 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.