colordemo

colordemo is a Python package implementing RGB queries on xterm-like terminals. It includes a demo script for presenting terminal color schemes, complete with RGB hex codes.

Quick start

There are many ways to run the demo script, and we will briefly describe them here. Note that with any of the methods below, the colordemo tool can accept command-line options. To see which options are available, use --help with any of the methods, e.g.,

pipx run colordemo --help

Using pipx

With only an active internet connection and the pipx Python utility, the script can be run directly without installation:

pipx run colordemo

Alternatively, it can also be installed explicitly and run that way:

pipx install colordemo
colordemo

Using pip

The package can also be installed and run as a normal Python package using pip (preferably in a virtualenv environment):

pip install colordemo
colordemo

# Equivalent
python -m colordemo

From the source tree

Finally, the script can be run easily from the source tree directly. This package has no dependencies besides Python, so no actions are needed besides cloning the repository.

git clone 'git@github.com:dranjan/python-colordemo.git'
cd python-colordemo
python -m colordemo

Overview of functionality

colordemo allows you to programmatically determine the RGB values of some terminals' ANSI colors (or more colors, if the terminal has them). The functions must be run from the terminal whose colors you want to determine, and with caveats if within a screen or tmux session (see below for more on this). Not all terminal types are supported (see the next section).

Terminal support

The fundamental requirement for a terminal to be supported by colordemo is for it to support the xterm-like OSC ("Operating System Command") control sequences, listed under "Operating System Commands" here:

https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h3-Operating-System-Commands

(Sometimes this support can be ascertained from the documentation of the terminal, but often you just need to try it.)

We call these terminals "xterm-like". If a terminal emulator doesn't support those sequences, then it won't be supported here. There may be other ways to obtain RGB values for these terminals, such as parsing configuration files or perhaps parsing the output of xrdb --query, but we have no plans to implement any of these. The only way to add support for a currently unsupported terminal is to patch the terminal with support for the OSC sequences.

There are too many terminals for us to test all of them, so the lists below are not exhaustive. If a terminal isn't mentioned in one of the following subsections, attempt at your own risk!

Fully supported terminals

• xterm
• urxvt
• VTE-based terminals, including:
  • vte
  • Terminal (XFCE)
  • gnome-terminal
  • terminator
  • tilda
  • (etc.)
• kitty
• alacritty
• wezterm
• ttyd
• (etc.)

Unsupported terminals

• Konsole-based terminals, which are buggy:
  • Konsole
  • yakuake
  • (etc.)
• terminology
• st (unpatched)
• Linux basic TTY (text mode without X)
• (etc.)

Some terminals (like terminology) don't seem to allow their colors to be queried dynamically, so all RGB queries will fail, but the failure can be detected. The demo script will therefore be able to output a color table, but without RGB values.

Other terminals (like Konsole) seem to support the query codes but are extremely buggy, returning incorrect values and even segfaulting sometimes.

In other cases (like the basic TTY), colordemo will garble the TTY and make it unreadable. (Try tput reset<ENTER> to restore it to something usable.)

Note regarding screen and tmux

It generally doesn't make sense to query a terminal from inside a screen or tmux session, since a single screen or tmux session can be attached to multiple terminals. However, in the special case of being attached to a single terminal, it is possible because tmux and screen provide (different) methods to pass control sequences through to the attached terminal. Of course, it makes no sense to try this if there are multiple terminals attached, and you should expect crazy results if you do. Thus, forwarding queries through screen or tmux is currently an opt-in feature (see the screen_forward optional argument in TerminalQueryContext.__init__ or the --screen-forward/--tmux-forward command-line options). This will fail inside a nested screen or tmux session.

(Not using the optional screen/tmux control-passthrough support, it's interesting to observe that screen and tmux emulate a 256-color terminal independently of the terminal(s) to which they are attached, which is very apparent if you run the script with 256-color output on a screen session attached to a terminal with 8- or 16-color terminfo (or with TERM set to such).)

Python API

For greater flexbility, the functionality of this package can also be accessed through its Python API. For example, this could be useful to create new color scheme demo scripts.

The primary interface is the context manager, colordemo.TerminalQueryContext. The color queries must be performed inside the context manager's context.

import colordemo

with colordemo.TerminalQueryContext() as tq:
    # Simplest method: get everything at once.
    # This provides a list of RGBAColor instances.
    colors = tq.get_all_indexed_colors()

    # Alternatively, you can query individual colors.
    n = tq.get_num_colors()
    colors = [tq.get_indexed_color(k) for k in range(n)]

    # The foreground and background colors need to
    # be queried separately:
    fg = tq.get_fg()
    bg = tq.get_bg()

# Color values are represented as instances of `RGBAColor`, which is
# a specialization of `namedtuple`.
(r, g, b, a) = fg

# Equivalent:
r, g, b, a = fg.r, fg.g, fg.b, fg.a

# Color components are floating-point numbers in the range [0, 1].
# To convert these to two-digit hex codes:
r_hex = '%02x' % (int(r * 0xffff) // 256)  # etc.

Credits

• dranjan: main implementation
• oblique: improved tmux support
• Xyne: much useful discussion and review