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

[buran]

just to mention that brackets in your if/elif/else conditions are redundant

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: