Arrows keys for getch in python

Question

I want to capture arrow keys in python linux:

   import getch as gh
   ch = ''
   while ch != 'q':
       print(ch)
       ch = gh.getch()
       k = ord(ch)
       print(k)
       # my question is:
       if k or ch = ???
          print("up")

When I run the code above and hit arrow keys, I get the following chars, what are they and how can I match one?

27

1
[
66
B
27

1
[
67
C
27

1
[
65
A

Answer 1

They are ANSI escape sequences.

When we execute the code below in a terminal:

import getch as gh

ch = ''
while ch != 'q':
    ch = gh.getch()
    print(ord(ch))

it prints the following when we hit the arrow up ↑ key once:

27
91
65

Referring ASCII table, we can see that it corresponds to ESC[A. It is the code for "Cursor UP" in ANSI escape sequences. (The sequence for CSI is ESC [, so ESC[A == CSI A == CSI 1 A which means "Moves the cursor one cell in the up direction.")

In the same way, we can figure out the other arrow keys also.

---

If you want to match arrow keys by using the getch module, you can try the following code (get_key function below is originally from this answer):

import getch as gh


# The function below is originally from: https://stackoverflow.com/a/47378376/8581025
def get_key():
    first_char = gh.getch()
    if first_char == '\x1b':
        return {'[A': 'up', '[B': 'down', '[C': 'right', '[D': 'left'}[gh.getch() + gh.getch()]
    else:
        return first_char


key = ''
while key != 'q':
    key = get_key()
    print(key)

which prints the following when we press ↑ ↓ ← → q

up
down
left
right
q