_curses.error: addwstr() returned ERR on changing nlines to 1 on newwin method

Question

The code is:

from curses import *
from curses.panel import *

def main(stdscr):
    start_color()
    curs_set(0)
    init_pair(1, COLOR_BLACK, COLOR_CYAN)

    posy = posx = 0
    window = newwin(1, 1, posy, posx)
    panel = new_panel(window)
    window.addstr('*', color_pair(1))
    update_panels()
    doupdate()

    while True:
        key = stdscr.getch()

        if key == ord('j'):
            posy+=1
        elif key == ord('k'):
            posy-=1
        elif key == ord('h'):
            posx-=1
        elif key == ord('l'):
            posx+=1
        elif key == ord('q'):
            endwin()
            break
        panel.move(posy,posx)
        update_panels()
        doupdate()
if __name__ == '__main__':
    wrapper(main)

I am getting this error:

Traceback (most recent call last):
  File "test_1_height_error.py", line 34, in <module>
    wrapper(main)
  File "/usr/lib/python3.7/curses/__init__.py", line 94, in wrapper
    return func(stdscr, *args, **kwds)
  File "test_1_height_error.py", line 12, in main
    window.addstr('*', color_pair(1))
_curses.error: addwstr() returned ERR

However if I change line 10 from window = newwin(1, 1, posy, posx) to window = newwin(2, 1, posy, posx) ie change the nlines args to greater than 1 then it works fine.

I really don't understand why I am getting this issue.

Answer 1

addch and anything built from it (such as addstr ) prints the text and advances the cursor past what was printed.

A 1x1 window isn't big enough to write one character and wrap to the next line (since you filled the line). When the window was 2x1 , it could do that.

ncurses (any X/Open Curses) has other functions (such as addchstr ) that don't advance the cursor, but I don't see those mentioned in the python curses reference .

Since ncurses will print the character that you want, and it's an isolated case, the workaround is to wrap the addstr in a try-statement, eg,

try:
    window.addstr('*', color_pair(1))
except curses.error:
    pass