Replace string in var

Question

I am using below code to replace a string, it is actually working, I want to know if there is better way to do it ? I just want to read data coming from serial, if it is same value do nothing but if it is new value print it...

new = ""
old = ""

while True:
    new = readQR("/dev/input/event7")
    if new != old:
        print (new)
        old = ""
        old = new
        new = ""
    else:
        new = ""

Couple of comments in here, in python you don't need to set the variable as empty in order to assign a new value, you could just do: old = new you don't need old="" and new="" also the else block is not needed — EnriqueBet
– EnriqueBet, Commented Mar 7, 2022 at 5:54
instead of the three lines you're using to swap old and new, you could do it in just one line, old, new = new, "" — Green Cloak Guy
– Green Cloak Guy, Commented Mar 7, 2022 at 5:57

anirudh sharma · Accepted Answer · 2022-03-07 06:29:52Z

1

I am guessing that you are new to Python. In case you already now these then it might help others :)

You can trim down your code to this:

new = ""
old = ""

while True:
    new = readQR("/dev/input/event7")
    if new != old:
        old, new = (new, "")  # tuple unpacking

We don't need to do new = "" in else condition as it would be overwritten by readQR in the next iteration.

Brief explanation of old, new = (new, ""):

Here what we are doing is that we are creating a tuple - (new, "") and unpacking it in old and new.

This example might help in understanding the concept of tuple unpacking-

>>> a = 1
>>> b = 2
>>>
>>> t = a, b  # t is a tuple
>>> t
(1, 2)
>>>
>>> b, a = t  # tuple unpacking - same as b = t[0] and a = t[1]
>>> b
1
>>> a
2

You can refer to this video - Tuples & Tuple Unpacking in Python

answered Mar 7, 2022 at 6:29

anirudh sharma

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1 Comment

Huismori Over a year ago

Thanks for reply, but it doesnt give me any output ; new = "" old = "" while True: new = readQR("/dev/input/event7") if new != old: old, new = (new, "") print (new) as I want to change old value with new value and if it is same value do nothing...

TheFaultInOurStars · Accepted Answer · 2022-03-07 08:57:30Z

1

I figured it out based on AnirudhSharma's answer:

old, new = ("", "")

while True:
    new = readQR("/dev/input/event7")
    if new != old:
        old = new
        print (new)

edited Mar 7, 2022 at 8:57

TheFaultInOurStars

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answered Mar 7, 2022 at 6:54

Huismori

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1 Comment

anirudh sharma Over a year ago

Nice that you got it working and welcome to Stack Overflow :)

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