Python for loop accessing GPIO pins

Question

I'm new to Python and the Raspberry Pi. I'm trying to shorten my code and use for loops for repetitive parts in my code, like changing all pins to high and low.

I'm trying to use a for loop to access pins. Is this even possible?

import RPi.GPIO as GPIO
from time import sleep

R1=22
R2=10
R3=9
R4=11

GPIO.setup(R1, GPIO.OUT)
GPIO.setup(R2, GPIO.OUT)
GPIO.setup(R3, GPIO.OUT)
GPIO.setup(R4, GPIO.OUT)

for x in range(1, 5):
    print "We're on time %d" % (x)
    GPIO.output(R + %d % (x), GPIO.HIGH)
    sleep(1)
    GPIO.output(R + %d % (x), GPIO.LOW)
    sleep(1)

GPIO.cleanup()

score 0 · Answer 1 · answered Apr 09 '15 at 07:15

0

That sort of thing is possible, but often nicer to use a list or dict:

pins = [22, 10, 9, 11]

for pin in pins:
    GPIO.setup(pin, GPIO.OUT)

for x in range(1, 5):
    GPIO.output(pins[x], GPIO.HIGH)
    sleep(1)
    GPIO.output(pins[x], GPIO.LOW)
    sleep(1)

answered Apr 09 '15 at 07:15

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That sort of thing *isn't* possible. They're trying to create a variable name dynamically: `R + '1'`, etc. – Peter Wood Apr 09 '15 at 07:44
@PeterWood They're just trying to access variables that already exist, which can be done using `eval`, `exec`, etc (but isn't very nice). – 101 Apr 09 '15 at 07:52
I see what you mean now. – Peter Wood Apr 09 '15 at 08:04

score 0 · Answer 2 · answered Apr 09 '15 at 07:16

You can't create variable names like that. You have to have the same variable name and change what it is pointing to:

pins = [R1, R2, R3, R4]

for pin in pins:
    GPIO.setup(pin, GPIO.OUT)

for pin in pins:
    GPIO.output(pin, GPIO.HIGH)
    sleep(1)
    GPIO.output(pin, GPIO.LOW)
    sleep(1)

Python for loop accessing GPIO pins

2 Answers2