Controlling GPIO in RPI via python 2 input

Question

This is a very simple question that I could not find the answer to via google. I just want to have an input, such as typing Green to turn on a green LED. Here is my code so far.

import RPi.GPIO as GPIO
import time
GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
GPIO.setup(21,GPIO.OUT)
GPIO.setup(26,GPIO.OUT)
GPIO.setup(17,GPIO.OUT)



Green = 'GPIO.output(17, True)'

input ()

Typing in green just says the string back. Without the '', it just runs the script and turns the LED on. Thanks for your hlep.

What search terms did you use? It’s odd that you couldn’t find anything relevant on google. — AMC, Dec 04 '19 at 02:41

dddJewelsbbb · Answer 1 · 2019-12-04T01:59:43.123

0

You need to capture your input in a variable, like so: color = input()

Then you can plumb that input through some logic:

if color.lower() == 'green':
    GPIO.output(17, True)

Here, I forced the input to be lowercase, so we only account for the input as if it were entered in lowercase, for easy comparison of strings since "Green" != "green"

Because there may still be confusion, I amended this answer with the following two examples:

A more complicated example, using a dictionary:

def set_color_green():
    # Sets green by calling the output function to the gpio object
    GPIO.output(17, True)

# construct a dictionary with valid values
gpio_func_dict = {'green': set_color_green} # Here, all we need is a function name

color = input()

# guard against capital letters
if color.lower() not in gpio_func_dict.keys():
    raise Exception('You provided an invalid option')

# Call the right function
gpio_func_dict[color.lower()]()

And a dangerous example using the string...

if color.lower() == 'green':
    exec(Green) # getting in the habit of doing this could lead to a long career of security flaws, vulnerabilities, and bugs

edited Dec 04 '19 at 01:59

answered Dec 04 '19 at 01:27

dddJewelsbbb

626
4
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Can you explain to me what input.lower is? Im super new to python, I apologize. – Zach Davis Dec 04 '19 at 01:33
I get this error. Traceback (most recent call last): File "/home/pi/Desktop/control.py", line 14, in if input.lower() == 'Green': AttributeError: 'builtin_function_or_method' object has no attribute 'lower' – Zach Davis Dec 04 '19 at 01:33
So, perhaps it's a wise idea to use a different variable name, like `color =` instead of `input =`, but that error shouldn't happen unless you don't create an `input`. Are you actually doing `input = input()` before you call `input.lower()`? – dddJewelsbbb Dec 04 '19 at 01:35
I created the input, however my output is just sending back the code I typed in.>>> Green 'GPIO.output(26, True)' – Zach Davis Dec 04 '19 at 01:40
This is python 2 by the way. – Zach Davis Dec 04 '19 at 01:40
I missed that this was Python2.x, but was surprised to find that masking a builtin like that didn't work in Python2.x. Regardless, I still don't understand your confusion -- perhaps I need to update my answer to add additional information. I think there's an expectation of executing a string -- which is possible if done a specific way, but is really a bad habit – dddJewelsbbb Dec 04 '19 at 01:44
Also, as a disclaimer: I never deal with GPIO. I assumed your issue was that you were calling `Green` inline or something like that. – dddJewelsbbb Dec 04 '19 at 01:45
Basically, I want python to execute something based off of the input I type in, I assume I would need to assign a variable, green in this case, to output my command in python. The GPIO command is just GPIO.output(17, True). By learning to do this, I hope to be able to go further in python/pi programming. – Zach Davis Dec 04 '19 at 01:52
@ZachDavis If you just want to _output_ it to the screen, then fine, print it. But if you want to _execute_ it, the example I have above should be more than sufficient to do just that. I'll even throw in a more complex example, AND a dangerous example! – dddJewelsbbb Dec 04 '19 at 01:53
@ZachDavis hth, I added two more examples of different ways to do what you're asking. The one in the middle is more "complete", whereas the last one is a modification to the if statement in the original. Definitely be careful, and doing the last one is *for educational purposes only*, I wouldn't get in the habit of doing that, because exec could be extremely dangerous under the right circumstances. – dddJewelsbbb Dec 04 '19 at 02:02

score 0 · Answer 2 · answered Dec 04 '19 at 02:06

It's best to use constants for your GPIO pin numbers. Then when you say change the green-LED to another pin, the code only needs to be changed at a single point.

I moved the GPIO setup code into a single function, and also made the setting of the green LED a function.

The main loop of the program prompts the user to input a command. If they type 'quit', the loop exits. If they type 'green' the LED will change state. The current state is held in the variable green_led.

There's an important difference in the input() function between Python2 and Python3. In Python2 it's best to use raw_input(), and not use input(). One you do have some user input, you need to clean it up to make checking easier. In the code below, the user_input is first trimmed of spaces with .strip(), and then all the letters are made lower-case with lower(), meaning something like "AbCDe" becomes "abcde". This allows us to check whether " GReen" equals "green" easily, and not have check a bunch of different letter-case combinations.

import RPi.GPIO as GPIO
import time

# Pin constants
PIN_GREEN  = 17
PIN_OTHER1 = 21
PIN_OTHER2 = 26

def setupGPIO():
    # Configure GPIO PINs
    GPIO.setwarnings( False )
    GPIO.setmode( GPIO.BCM )
    GPIO.setup( PIN_OTHER1, GPIO.OUT )
    GPIO.setup( PIN_OTHER2, GPIO.OUT )
    GPIO.setup( PIN_GREEN,  GPIO.OUT )

def setGreenPin( status ):
    """ Turn the Green-LED's PIN High or Low """
    if ( status == True ):
        GPIO.output( PIN_GREEN, True )
    else:
        GPIO.output( PIN_GREEN, False )

### Main Loop

# Set the initial state
setupGPIO()
setGreenPin( False )  # start with the LED off

done      = False
green_led = False

# Loop around, reading user commands until they enter 'quit'
while not done:
    user_input = raw_input( "Colour> " )       # get input form the user
    # user_input = input( "Colour> " )         -- python3
    user_input = user_input.strip().lower()    # trim spaces, make all lower-case
    # What did the user say?
    if ( user_input == 'quit' ):               # Is the user quitting?
        done = True            
    elif ( user_input == 'green' ):
        green_led = not green_led              # flip On <-> Off, and vice-versa
        setGreenPin( green_led )

Controlling GPIO in RPI via python 2 input

2 Answers2