How to refresh curses window correctly?

Question

while 1:
    ...
    window.addstr(0, 0, 'abcd')
    window.refresh()
    ...

window size is full terminal size, big enough to hold abcd. If 'abcd' is modified to shorter string like 'xyz', then on terminal I will see 'xyzd'. What exactly I am doing wrong?

Answer 1

Let's suppose you have this code, and you just want to know how to implement draw():

def draw(window, string):
    window.addstr(0, 0, string)
    window.refresh()

draw(window, 'abcd')
draw(window, 'xyz')  # oops! prints "xyzd"!

The most straightforward and "curses-ish" solution is definitely

def draw(window, string):
    window.erase()  # erase the old contents of the window
    window.addstr(0, 0, string)
    window.refresh()

You might be tempted to write this instead:

def draw(window, string):
    window.clear()  # zap the whole screen
    window.addstr(0, 0, string)
    window.refresh()

But don't! Despite the friendly-looking name, clear() is really only for when you want the entire screen to get redrawn unconditionally, i.e., "flicker". The erase() function does the right thing without flicker.

Frédéric Hamidi offers the following solutions for erasing just part(s) of the current window:

def draw(window, string):
    window.addstr(0, 0, string)
    window.clrtoeol()  # clear the rest of the line
    window.refresh()

def draw(window, string):
    window.addstr(0, 0, string)
    window.clrtobot()  # clear the rest of the line AND the lines below this line
    window.refresh()

A shorter and pure-Python alternative would be

def draw(window, string):
    window.addstr(0, 0, '%-10s' % string)  # overwrite the old stuff with spaces
    window.refresh()