Using the curses library to view IoT data
Curses Windows
The examples so far have been based on a main screen object, but the curses library also supports windows. Windows are useful because they support border outlines, and text can be cleared from and written to windows without affecting the main screen object. The syntax to create a curses window object is:
mynewwindow = curses.newwin( height, width, begin_y, begin_x)
The code for Figure 3,
# define a win1 window object win1 = curses.newwin(9, 44, 6, 4) # write text inside the window object win1.addstr(8,0, "Sensor 1: Temperature Reading", curses.A_BOLD) value1 = pyfiglet.figlet_format( "23 C", font = "doom") win1.addstr(0,0,value1,curses.color_pair(2) )
produces two curses windows. The major difference in the code is that information within a window is addressed by the window object instead of the background screen object.
Dynamic Bars
Simple progress or indicator bars can be created by a curses window with a border (Listing 4). The bar itself is generated by writing a space character with inverse video (Figure 4).
Listing 4
bar.py
01 import curses 02 03 bar = ' ' # with reverse video a space will show up 04 value1 = 10 # in real life this needs to be scaled 05 06 stdscr = curses.initscr() 07 curses.curs_set(0) # don't show the cursor 08 09 stdscr.addstr(1,3, "Python Curses Bar") 10 stdscr.refresh() 11 # Define windows 12 win1 = curses.newwin(3, 32, 3, 2) 13 win1.border(0) # add a border 14 # a horizontal bar 10 characters wide 15 win1.addstr(1, 1, bar * value1,curses.A_REVERSE ) 16 win1.refresh() 17 18 # Wait for a key press then exit 19 stdscr.getch() 20 curses.endwin() # restore the terminal to original settings
After I had the basic curses bar working, I was able to use what I learned in the earlier examples to create Raspberry Pi interfaces that included color and large text (Figure 5).
Summary
If you are looking for a quick and easy way to present data, without the bother of a GUI, curses is a great solution. Curses is supported in a variety of programming languages. I focused my curses work here on C and Python, but I've also had good success in Lua.
I only had one presentation issue and that was with line drawing characters like borders when I used Putty (a Windows-based SSH program). To fix this issue, I changed the Putty Window | Translation setting to use the VSCII character set; then, everything looked good.
Infos
- Python curses: https://docs.python.org/3/library/curses.html
- Code for this article: ftp://ftp.linux-magazine.com/pub/listings/linux-magazine.com/232/
- pyfiglet: https://github.com/pwaller/pyfiglet
- FIGlet fonts: http://www.figlet.org/examples.html
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