two button reaction game using python3 and raspberry pi3

Question

First post and and only been learning Python for 3 weeks...

I'm trying to create a game where 2 players have to wait for a buzzer sound connected to a breadboard and then press a button to see who is first.

This worked fine until I tried to add a method of keeping score. Now when the game runs the buzzer doesn't stop when the button is pressed and I get several error messages that repeat in the window. Can anyone help me to see what I've done wrong please?

from gpiozero import Button, LED, Buzzer
from time import time, sleep
from random import randint

led1 = LED(17)
led2 = LED(27)
btn1 = Button(14)
btn2 = Button(15)
buz = Buzzer(22)
score1 = 0
score2 = 0

btn1_name = input('right player name is ')
btn2_name = input('left player name is ')

while True:
    print(btn1_name + ' ' + str(score1) + ' - ' + btn2_name + ' ' + str(score2))
    sleep(randint(1,10))
    buz.on()
    def pressed(button):
        if button.pin.number == 14:
            print(btn1_name + ' won the game')
            score1 += 1
        else:
            print(btn2_name + ' won the game')
            score2 += 1
        buz.off()
    btn1.when_pressed = pressed
    btn2.when_pressed = pressed

The output messages are as follows

dave 0 - keith 0
keith won the game
Traceback (most recent call last):
  File "/usr/local/lib/python3.4/dist-packages/gpiozero/pins/rpigpio.py", line 232, in <lambda>
    callback=lambda channel: self._when_changed(),
  File "/usr/local/lib/python3.4/dist-packages/gpiozero/mixins.py", line 311, in _fire_events
    self._fire_activated()
  File "/usr/local/lib/python3.4/dist-packages/gpiozero/mixins.py", line 343, in _fire_activated
    super(HoldMixin, self)._fire_activated()
  File "/usr/local/lib/python3.4/dist-packages/gpiozero/mixins.py", line 289, in _fire_activated
    self.when_activated()
  File "/usr/local/lib/python3.4/dist-packages/gpiozero/mixins.py", line 279, in wrapper
    return fn(self)
  File "/home/d.chilver/twobuttonreaction.py", line 26, in pressed
    score2 += 1
UnboundLocalError: local variable 'score2' referenced before assignment
dave 0 - keith 0

Sören Titze · Accepted Answer · 2017-03-15 16:59:02Z

1

The problem is a problem of scoping. The two variables score1 and score2 are in the so called global scope. But you want to use them locally in a function. Python tries to create a local variable called score1 or score2 respectively by assigning a local variable score1 or score2 and then adding 1. Since the variable does not exist yet, you are subjected to the error message that you see.

In order to access the global variables you have to mark them explicitly like this:

[...]
def pressed(button):
    global score1
    global score2
    if button.pin.number == 14:
        print(btn1_name + ' won the game')
        score1 += 1
    else:
        print(btn2_name + ' won the game')
        score2 += 1
    buz.off()
[...]

answered Mar 15, 2017 at 16:59

Sören Titze

1,0051 gold badge15 silver badges32 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Dave Chilver Over a year ago

Thanks for the answer! It was a big help. Just as a follow up... are global variables like my original ones bad practice? My next step is to stop the game accepting spam inputs. As it stands the player can hammer the button and receive a +1 score each time regardless of when the buzzer sounds. Any ideas would be a great help.

Sören Titze Over a year ago

There is no problem with using global variables. Check out this gist: gist.github.com/NemoNessuno/1121acc79823f1d54dc83f8258118162 for some ideas regarding the input spam. Please note that I did not check the code because I'm at work right now, so if you encounter some problems please send me a message.

Collectives™ on Stack Overflow

two button reaction game using python3 and raspberry pi3

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related