How can I Have if statement output result into python script

Question

I am trying to implement a light sensors input so it outputs a value in the larger python script.

Specifically print the LED_BRIGHTNESS = 75 or LED_BRIGHTNESS = 255

Basically I when this script runs I want the sensor to dictate the LED brightness for the string of LED's

I started out trying to do the following...

import urllib2
import xml.etree.ElementTree as ET
import time
from neopixel import *
import sys
import os    
import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM)
GPIO.setup(4,GPIO.IN)

if GPIO.input(4) == 1:
        print "LED_BRIGHTNESS = 75"
else:
        print "LED_BRIGHTNESS = 255"
# LED strip configuration:
LED_COUNT      = 95      # Number of LED pixels.
LED_PIN        = 18      # GPIO pin connected to the pixels (18 uses PWM!).
#LED_PIN        = 10      # GPIO pin connected to the pixels (10 uses SPI /dev/spidev0.0).
LED_FREQ_HZ    = 800000  # LED signal frequency in hertz (usually 800khz)
LED_DMA        = 5       # DMA channel to use for generating signal (try 5)
#LED_BRIGHTNESS = 255     # Set to 0 for darkest and 255 for brightest
LED_INVERT     = False   # True to invert the signal (when using NPN transistor level shift)
LED_CHANNEL    = 0       # set to '1' for GPIOs 13, 19, 41, 45 or 53
LED_STRIP      = ws.WS2811_STRIP_GRB   # Strip type and colour ordering

That would output the result into the terminal, but I need it to output into the larger script.

So then I tired the following...

import urllib2
import xml.etree.ElementTree as ET
import time
from neopixel import *
import sys
import os
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(4,GPIO.IN)


if GPIO.input(4) == 1: "LED_BRIGHTNESS = 75"
if GPIO.input(4) == 0: "LED_BRIGHTNESS = 255"


# LED strip configuration:
LED_COUNT      = 95      # Number of LED pixels.
LED_PIN        = 18      # GPIO pin connected to the pixels (18 uses PWM!).
#LED_PIN        = 10      # GPIO pin connected to the pixels (10 uses SPI /dev/spidev0.0).
LED_FREQ_HZ    = 800000  # LED signal frequency in hertz (usually 800khz)
LED_DMA        = 5       # DMA channel to use for generating signal (try 5)
#LED_BRIGHTNESS = 255     # Set to 0 for darkest and 255 for brightest
LED_INVERT     = False   # True to invert the signal (when using NPN transistor level shift)
LED_CHANNEL    = 0       # set to '1' for GPIOs 13, 19, 41, 45 or 53
LED_STRIP      = ws.WS2811_STRIP_GRB   # Strip type and colour ordering

This returns the following error.

Traceback (most recent call last):
  File "metar.py", line 30, in <module>
    strip = Adafruit_NeoPixel(LED_COUNT, LED_PIN, LED_FREQ_HZ, LED_DMA, LED_INVERT, LED_BRIGHTNESS, LED_CHANNEL, LED_STRIP)
NameError: name 'LED_BRIGHTNESS' is not defined

I am so new at this I don't even know what the correct terminology to use when trying to google the problem. I tried looking at how to print if statement output into string, or how to output if statement into string and I keep finding things that talk about completely predefined values not something coming from a sensors if statement.

If someone could point me in the right direction I'd appreciate it.

Surely you didn't mean to just wrap your code in a string...? — tyteen4a03
– tyteen4a03, Commented Apr 9, 2018 at 0:28
I think so. I need it to output so the LED_BRIGHTNESS value is based off the sensor input. — Bill
– Bill, Commented Apr 9, 2018 at 0:34
You just want to set the variable dynamically? Its just LED_BRIGHTNESS = 75 if GPIO.input(4) == 1 else 255. — tdelaney
– tdelaney, Commented Apr 9, 2018 at 0:38
Thanks, I figured this would be stupid easy, just no clue here. Really appreciate your time. — Bill
– Bill, Commented Apr 9, 2018 at 0:41

tdelaney · Accepted Answer · 2018-04-09 00:43:10Z

1

It looks like you want to set a variable dynamically. In this case, since there are only two possible values, an inline if will do:

LED_BRIGHTNESS = 75 if GPIO.input(4) == 1 else 255

Or you could expand the if:

if GPIO.input(4) == 1:
    LED_BRIGHTNESS = 75
else:
    LED_BRIGHTNESS = 255

answered Apr 9, 2018 at 0:43

tdelaney

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