BottomBar

Bottombar is a Python module that facilitates printing a status line at the bottom of a terminal window. The module functions as a state machine, and allows multiple, individually submitted status items to be displayed simultaneously.

Requirements

A VT100-capable terminal is required. Most Linux terminals qualify, including Xterm, Rxvt, Gnome terminal, Kitty terminal, and Alacritty. On MS Windows the new Windows Terminal is recommended.

Other than this BottomBar has no dependencies beyond Python version 3.3.

How to use it

A bar entry is created using the module's add context, and displayed for the duration that the context is entered. It also activates an event handler that reformats and redraws the bar whenever the terminal window is resized.

>>> import bottombar as bb
>>> 
>>> with bb.add('bottom bar', label='powered by') as item:
...     print('regular output')
# regular output                                                              #
# powered by: bottom bar                                                      #

Items can be modified in place:

...     item.text = 'bottom bar v2'
# powered by: bottom bar v2                                                   #

Labels are optional, and multiple items can be stacked:

...     with bb.add('more bar text'):
# regular output                                                              #
# powered by: bottom bar v2 | more bar text                                   #

Items can be right-aligned:

...         with bb.add('12:00', label='time', right=True):
# regular output                                                              #
# powered by: bottom bar v2 | more bar text                       time: 12:00 #

If items no longer fit the bar then labels are dropped to make room:

...             with bb.add('more right-aligned bar text', right=True):
# regular output                                                              #
# bottom bar v2 | more bar text           more right-aligned bar text | 12:00 #

If this is not enough, long text entries are truncated:

...                 with bb.add('this is getting too much'):
# regular output                                                              #
# bottom bar v2 | more bar text | this is gettin..   more right-ali.. | 12:00 #

The bar is automatically redrawn whenever its contents change. Content that changes dynamically can be refreshed at a configured rate:

>>> import time
>>> class Clock:
...     def __str__(self):
...         return time.strftime('%H:%M:%S')
>>> with bb.add(Clock(), label='time', right=True, refresh=1):
#                                                              time: 12:00:00 #
#                                                              time: 12:00:01 #
#                                                              time: 12:00:02 #

In case multiple refresh rates are configured simultaneously, the fastest rate prevails.

Technical details

The status line is positioned, and kept in position, using VT100 escape sequences. By configuring a scroll region that excludes the bottom line, regular output will scroll above it without further intervention.

The implementaton of automatic redrawing depends on the platform. On Unix-like systems both resize events and the redraw rate are handled using signals: SIGWINCH and SIGALRM. Pre-existing handlers for the former remain active, while those for the latter are disabled for the duration that a bar is active. On other platforms a thread is spawned that polls the terminal size once every second, as well as redraws the bar at the configured interval.