python unboundlocalerror

[ground_]

Hello all,

last week I red a book about writing in python and did some tutorials. Now i am getting the hang of it, and I wanted to write a program which guide me through some steps in order to turn on my LED light. But now i am experiencing an error which I can't figure out (but seems quite simple):

I wrote the following code:

Code: Select all

def led():
    import RPi.GPIO as GPIO
    import os
    print ("please input which mode to use for GPIO pin Numberering: \n")
    print ("1 = BOARD")
    print ("2 = BCM")
    print ("\n")
    smode = input("please enter you choice: ")

    if smode == "1":
        mode="BOARD"
    elif smode == "2":
        mode="BCM"
    else:
        print ("no valid choice, please select '1' or '2'")
        os.system("clear")
        led()

    print("selected: >>> ", mode)
    input()

now this is my error:
the first run goes ok, if i select 1 or 2 it will show me which mode i selected, and goes on with the script after i press enter.

But when i select something else then 1 or 2, it will start from the beginning of the function (so it is still doing what I want). When i select 1 or 2 now, it will still print the ("selected: >>>", mode) fine, but also gives an error and closes the program (instead of going on with the script).

the error is as following:

Code: Select all

File "options.py", line 44, in led
    print("selected: >>> ", mode)
UnboundLocalError: local variable 'mode' referenced before assignment

now i cant figure out why it is doing this, can anybody here explain it maybe?

thanks in advance!

[DougieLawson]

Code: Select all

    if smode == "1":
        mode="BOARD"
    elif smode == "2":
        mode="BCM"
    else:
        print ("no valid choice, please select '1' or '2'")
        os.system("clear")
        led()

What happens if smode != "1" AND smode != "2" you don't set a default value for mode.

Code: Select all

    if smode == "1":
        mode="BOARD"
    elif smode == "2":
        mode="BCM"
    else:
        print ("no valid choice, please select '1' or '2'")
        mode = "INVALID"  # set a bad value when smode isn't 1 or 2
        os.system("clear")
        led() 

[ground_]

well, i thought it would go to the else function then (and restart at the beginning), but defining it would be a good idea.

well i think I (accidentally) figured it out:
I simply put a return at the end of the ELSE: block. Other wise the functions keeps running while it started again (and 2 are running at the same time).

[elParaguayo]

Another way to do it, without calling the led() function again would be as follows:

Code: Select all

smode = None

while not smode in ["1", "2"]:

    smode = input("please enter you choice: ")

    if smode == "1":
        mode="BOARD"
    elif smode == "2":
        mode="BCM"
    else:
        print ("no valid choice, please select '1' or '2'")
        os.system("clear")