Barcode batch scanning - why does this code require a double scan to terminate?

Question

I am a novice Python programmer, trying to write a Python script to run a barcode scanning station (Raspberry Pi 4, RPiOS, Python 3.7.3). I want to scan a certain number of items, and when complete I want to scan a different barcode to process the input. From there either it will send a GPIO signal if batch count is met, or terminate the program outright if the count is too high or low.

I have been successful with what I've written, with one exception: when a second barcode is scanned to process the input, it needs to be scanned TWICE to trigger the rest of the script. I'm stumped as to why this is, and am sure this is something simple I overlooked.

import RPi.GPIO as GPIO
GPIO.setwarnings(False)
import time

good = 38

GPIO.setmode(GPIO.BOARD)

GPIO.setup(good,GPIO.OUT)
GPIO.output(good,GPIO.HIGH)

try:
    def batch_order():

        batch = input("Enter the number of parts on the order: ")
        barcode1 = input("Scan MASTER barcode: ")
        print("Begin scanning barcodes: ")
        count = 0
    
        while True:
            
            if input() == barcode1:
                count+= 1
                print("Part count: %s"%(str(count)))
            elif input() != barcode1:
                time.sleep(0.2)
                if batch == str(count):
                    print("Order complete! Now printing shipping label...")
                    time.sleep(0.2)
                    GPIO.output(good,False)
                    time.sleep(15)
                    GPIO.output(good,True)
                    break
                else:
                    print("Order incorrect, %s of %s parts scanned."%(str(count), batch))
                    time.sleep(2)
                    break
            
    batch_order()

except KeyboardInterrupt:
    
    GPIO.cleanup()
    print("QUIT")
    GPIO.cleanup()

All I want to do is eliminate the double scan required to terminate the program at elif input() != barcode1:. Any help would be greatly appreciated, thank you!

score 2 · Answer 1 · answered May 04 '21 at 18:34

2

Just get the input() once and assign it

value = input()

if value == barcode1:
   ...
else:  # there is also no other case
   ...

answered May 04 '21 at 18:34

ti7

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By eliminating the `input` in the `else` clause, you've also eliminated the need to assign the string to a variable. – Mark Ransom May 04 '21 at 18:42
1

indeed! though I think as it's so trivial they'll manage – ti7 May 04 '21 at 18:47
Yep, it was something simple. This did the trick nicely. Thanks so much, everyone! – MPC_Quality May 05 '21 at 12:47
@MPC_Quality if this solved your Question, please mark it as the Answer with the check to its left! – ti7 May 07 '21 at 18:54

Barcode batch scanning - why does this code require a double scan to terminate?

1 Answers1