Weird python bug. Variable changes value without any modification

Question

In the function "enText" changes its value even though I don't modify it.

e = 5 and n = 6. enText is an array of ints. I modify the values in the array after passing it to changeTxt. I then return changeTxt but for some reason enText ends up being modified as well.

No idea why.

#Function for encryption
    def encrypt(e, n, enText):

        #e=5 & n=6
        changeTxt = enText

        print(enText)
        #prints [18, 15, 2, 9, 14]

        for x in range(0, len(changeTxt)):

            #problem here!!!!!!!!
            tmp = changeTxt[x]**e
            tmp = tmp % n
            changeTxt[x] = tmp

        print(enText)
        #prints [0, 3, 2, 3, 2]

        return changeTxt

Possible duplicate of List of lists changes reflected across sublists unexpectedly — Mr. T
– Mr. T, Commented Apr 23, 2018 at 23:47

Ralf · Accepted Answer · 2018-04-23 23:47:19Z

1

Your line

changeTxt = enText

only copies the reference to the list, but both point to the same list. So changes to changeTxt will affect enText as well.

Instead try to clone the list like this:

changeTxt = enText[:]

or

changeTxt = list(enText)

answered Apr 23, 2018 at 23:47

Ralf

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1 Comment

Keith Over a year ago

Just did. Unfortunately I'm a new user so StackOverflow doesn't display my upvotes.

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