Correct usage of try and except(error) in python [duplicate]

Question

I was wondering how was the correct usage of the try execpt/execpt(err) function in python and why it's raising up this error

UnboundLocalError: cannot access local variable 'player_move'

where it is not associated with a value?? Here's the code:

Main text

def enter_move(board):
    try:
        player_move = int(input("Enter a number from 1 ~ 9: "))
    except ValueError:
        print("Invalid input, you can only enter intergers.")
    except:
        print("Invalid input.") # it's not finish here...

I've tried

result = None
try:
    value_str = "456"
    temp_result = int(value_str)
except ValueError:
    print("Invalid input for conversion.")
else:
    result = temp_result # Assign if no exception occurred

print(f"The result is: {result}")

but didn't work

perhaps though you name player_move, your function doesn't ever return player_move? — ti7
– ti7, Commented Sep 29 at 4:23
Specifically you may be running into a scoping issue when you name an outer (generally global) scope name player_move, but provide a path in a function whereby it can take either a local or the global name .. just removing the outer name (there is no need to forward declare in Python and often a different name will do nedbatchelder.com/text/names.html) or declaring the name global before using it in the function may clear this up (often a worse option as it's unnecessary and makes scopes and the source of changes more difficult to understand to future code contributors) — ti7
– ti7, Commented Sep 29 at 4:40
always put full error message (traceback) because there are other useful information. — furas
– furas, Commented Sep 29 at 8:49
this part of code seems OK. You may have problem in different place but you didn't show FULL error message and hard to say where it is. — furas
– furas, Commented Sep 29 at 8:52

ti7 · Accepted Answer · 2025-09-29 04:33:45Z

0

A more complete function might look like this

def enter_move():  # board arg isn't used, should it be or is there more?
    while True:  # consider limited retries like `for _ in range(5):\nelse:`
        player_move = input("Enter a number from 1 ~ 9: ")
        try:
            player_move = int(player_move)
        except ValueError:   
            if "q" in player_move.lower():  # consider a way to escape loop
                sys.exit("user quit")  # or something less-drastic!
            print("Invalid input, you can only enter intergers.")
        else:  # didn't raise
            break  # leave while loop
    return player_move

answered Sep 29 at 4:33

ti7

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2 Comments

jackal Sep 29 at 7:17

Maybe "q" == player_move.lower() to differentiate from input such as "torque"

ti7 Sep 29 at 7:23

@Ramrab of course in a more serious example (and we should note [Qq] to quit in the prompt line!), really there won't be many users and any that are providing anything non-numeric likely they aim to test functionality or leave

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