Python – Randomly replaces characters in a string with characters other than the current one

Let’s say I have a string and I want to modify it randomly with a set of options defined in another string. First, I created the original string and possible replacement characters:

string1 = "abcabcabc"
replacement_chars = "abc"

Then I found this feature to randomly replace n characters on the forum :

def randomlyChangeNChar(word, value):
     length = len(word)
     word = list(word)
     # This will select the distinct index for us to replace
     k = random.sample(range(0, length), value) 
     for index in k:
         # This will replace the characters at the specified index with the generated characters
         word[index] = random.choice(replacement_chars)
# Finally print the string in the modified format.
return "".join(word)

Except for an exception, this code does what I want — it doesn’t take into account characters in string1 that match random replacement characters. I know the problem is in the function I’m trying to tweak, I’m predicting under a for loop, but I’m not sure what to add to prevent the replacement character from equaling the old character in string1. Thanks for all the advice, please educate me if I make things too complicated!

In the function you retrieved, replace :

word[index] = random.choice(replacement_chars)

with

word[index] = random.choice(replacement_chars.replace(word[index],'')

Will get the job done. It simply replaces word[index] (the character you want to replace) with an empty string in the replacement_chars string, effectively removing it from the replacement character.

Another method, which is expected to be less efficient on average, is to redraw until you get a different character than the original:

That is, replace:

word[index] = random.choice(replacement_chars)

with

char = word[index]
while char == word[index]:
    char = random.choice(replacement_chars)
word[index] = char

or

while True:
    char = random.choice(replacement_chars)
    if char != word[index]:
        word[index] = char
        break

Warning: If the replacement_chars has only 1 character, both methods will fail when the original character is the same as the replacement character!