Python Curses - Detecting the Backspace Key

user_5265403 0
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I'm having a difficult time with detecting the Backspace key using the Curses module. Whenever I press the Backspace key, the character / string returned is '^?', however I'm not able to detect it with:

if str(key) == '^?':

The code below is set up to run

import curses

def main(win):
    win.nodelay(True)
    key = ''
    record = ''
    win.clear()
    win.addstr("Key:")
    win.addstr('\n\nRecord:')
    win.addstr(record)
    while True:
        try:
            key = win.getkey()

            if str(key) == '^?':
                # Attempt at detecting the Backspace key
                record = record[:-1]

            elif str(key) == '\n':
                # Attempt at detecting the Enter Key
                record = ''

            else:
                record += str(key)
            win.clear()
            win.addstr("Key:")
            win.addstr(str(key))
            win.addstr('\n\nRecord:')
            win.addstr(record)
            if key == os.linesep:
                break
        except Exception as e:
            # No input
            pass

curses.wrapper(main)
# CTRL+C to close the program
macos-high-sierra python-curses python-3.x python
3 Answers

According to your clarifying comment, backspace in your terminal is neither 'KEY_BACKSPACE' nor '\b' ('\x08').

Since you're using curses.wrapper(), which calls curses.initscr(), this suggests that something is wrong with either your terminfo database (unlikely) or your terminal configuration (more likely).

getkey() == 'KEY_BACKSPACE' or getch() == curses.KEY_BACKSPACE is supposed to work on any properly-configured system, so you're likely to have problems in other applications too.

The TERM environment variable is how the terminal type is communicated to tools which need the functionality beyond basic teletype, so, to fix that, start by checking what the TERM environment variable contains in the environment where you're running Python.

print(os.environ['TERM'])

As a quick hack, you can check all the values it's been observed to take.

if key in ('KEY_BACKSPACE', '\b', '\x7f'):
user_4352530

On my machine, running Python 3.5.2 or 2.7.12, I get KEY_BACKSPACE shown as the key when I press backspace, and using

if str(key) == 'KEY_BACKSPACE':

in place of

if str(key) == '^?':

results in the backspace key backspacing letters off record.

I think it's possible that, on your system, you're getting the actual backspace character. In that case, you might try '\b' in place of '^?', as according to the docs, that is the string escape for the ASCII backspace character.

user_22434950

In MacOS, please try this:

    key = w.getch()
    if key == 127:
        print("You've pressed Backspace")
user_24950540
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