Replacing a specific item in a string when that item occurs more than once, in Python-CodePudding

Let's say I have the following:

str1='restart'

I want to replace 'r' with '#' but only the second occurrence of 'r' and not the first, using the function replace()

Expected return is:

str1='resta#t'

I know how to replace either all the occurrences of 'r' str1.replace('r','#'), or a number of occurrences of 'r' starting from the first one str1.replace('r','#',1), but cannot figure how to replace just the second occurrence and not the other ones.

CodePudding user response：

If this doesn't solve the problem then I need more detail.

str1.replace(str1[5],'#')

r2 = str1.find(r, 2)
str1.replace(r2, '#')

CodePudding user response：

The following code does the trick.

string = "restart"
result = string.replace("r", "#").replace("#", "r", 1)
print(result) # resta#t

CodePudding user response：

You can use split and replace for the same.

str1 = "restart"
split_ch = "r"
new_ch = "#"
split_list = str1.split(split_ch, 1)
result = split_list[0]  split_ch   split_list[1].replace(split_ch,new_ch, 1)

CodePudding user response：

We can use a regex replacement here:

str1 = "restart"
output = re.sub(r'r([^r]*)r', r'r\1#', str1, 1)
print(output)  # resta#t

The pattern matches the first r, captures optional non r following letters, followed by the second r. We then replace, swapping in # for the second r. Note that the fourth parameter to re.sub is 1, meaning that this replacement will only happen once.

CodePudding user response：

str1='restart'
str1 = [*str1]
i = 0
j = 0
for string in str1:
    j  = 1
    print(string, j)
    if string == 'r':
        i =1
        if i ==2:
            str1[j-1] = '#'
        else:
            continue
print(''.join(str1))

Definitely not the best, but this works...

CodePudding user response：

One way that maybe gets it done for you!

def replace_second(input_:str, letter:str = 'r', replace:str ='other'):
    idx = [i for i, _ in enumerate(input_) if _ ==letter]
    return input_[:idx[1]]   input_[idx[1]:].replace(letter, replace)

Try it out yourself:

replace_second('restart', 'r', '#')