How to judge that the cross key is input in Python3

Introduction

You can determine the key by using the curses module. Here's a method that doesn't depend on it https://docs.python.org/ja/3/library/curses.html#constants

Preface

This is a memo for myself. It's a straightforward implementation. What I want to do is detect that a special character such as the cross key has been entered.

Knowledge of Unicode control characters is desirable as a prerequisite. wikipedia

Where it gets stuck

getch gets the input character by character. However, the arrow keys had to be entered three times. For example, the up arrow says 27 91 65. If nothing is done, not only will it not be possible to determine special keys such as arrow keys, but it will also receive unwanted input. Therefore, I implemented it as follows.

Source

getch Function that accepts one-character input ord is a function that converts characters to Unicode, chr is a function that converts Unicode to characters. The code is redundant, which doubles as a debug for myself.

#Prepare a function that receives input character by character instead of input.
#try for Windows, except Nonaka for Linux
try:
    from msvcrt import getch
except ImportError:
    import sys
    import tty
    import termios
    def getch():
          
            fd = sys.stdin.fileno()
            old = termios.tcgetattr(fd)
            try:
                tty.setraw(fd)
                return sys.stdin.read(1)
            finally:
                termios.tcsetattr(fd, termios.TCSADRAIN, old)

#Unicode control character aliases
EOT = 3
TAB = 9
ESC = 27

#Main loop
while True:
    key = ord(getch())
    if key == EOT:
        break
    elif key == TAB:
        print('keydown TAB')
    elif key == ESC:
        key = ord(getch())
        if key == ord('['):
            key = ord(getch())
            if key == ord('A'):
                print('keydown uparrow')
                continue
            elif key == ord('B'):
                print('keydown downarrow')
                continue
            elif key == ord('C'):
                print('keydown leftarrow')
                continue
            elif key == ord('D'):
                print('keydown rightarrow')
                continue
    else:
        message = f'keydown {chr(key)}'
        print(message)

Result of execution

You can see that the judgment has been taken properly.

At the end

This time, I didn't implement it because the code becomes redundant, but if you look at the Unicode when you enter a special key and enumerate all of them with conditional branching, you can make a judgment. The similar code in this article may be useful when building your own application. If anyone else knows a good way to write, please let me know.

reference

• https://torina.top/detail/428/
• https://stackoverflow.com/questions/12175964/python-method-for-reading-keypress