Question

running a program I am making to draw with turtle graphics, I put in an exit command, however now whenever I enter any single-word commands I get an indexerror (IndexError: list index out of range) at the elif for the “back” command:

def parse_line(line):
    global items_in_line
    items_in_line = line.split(" ",1)
    if items_in_line[0] == "forward":
        if isinstance(items_in_line[1], int):
                return items_in_line
    elif items_in_line[0] == "back" or "backward":
        if isinstance(items_in_line[1], int):
             return items_in_line
    ...
    elif items_in_line[0] == "exit":
        sys.exit()

line=input("Enter a turtle command or enter 'file' to load commands from a file")

x = parse_line(line)

Why? and how can I fix this?

Answer 1

elif items_in_line[0] == "back" or "backward":

the above condition is equivalent to: –

elif (items_in_line[0] == "back") or "backward":

Which will always be evaluated to true, and thus will also be executed if you pass “exit” as input, and hence items_in_line[1] will throw IndexError.

You need to change the condition to: –

elif items_in_line[0] in ("back", "backward"):