code not working, NameError: name 's' is not defined

[Yoriz]

In the __init__ you create a local s and try to use a local s in the method KLD2Setup
As you are now using a class you need to use self.s

#! /usr/bin/python
from serial import Serial

class RD():
    '''RFB K-LD2 module'''      
    def __init__(self, command):
        '''initialize'''
        self.cmd = command
        self.s = Serial('/dev/ttyS0', 38400)
 
    def KLD2Setup(self):
        '''use this method for sending commands and receiving data'''
        self.cmd = '$' + self.cmd + '\r'
        if (self.cmd[1] in {"S","D","R","W","T"}):
            k = 8
        elif (self.cmd[1] in {"F","A"}):
            k = 10
        elif (self.cmd[1] == "C"):  
            k = input ("Enter the number of bytes? ")   
        else: 
            k = 0
        if (k):
            self.s.write(self.cmd.encode())
            print((self.s.read(int(k)).rstrip()).lstrip(b'@'))