Replacing instances of a character in a string

This simple code that simply tries to replace semicolons (at i-specified postions) by colons does not work:

for i in range(0,len(line)):
     if (line[i]==";" and i in rightindexarray):
         line[i]=":"

It gives the error

line[i]=":"
TypeError: 'str' object does not support item assignment

How can I work around this to replace the semicolons by colons? Using replace does not work as that function takes no index- there might be some semicolons I do not want to replace.

Example

In the string I might have any number of semicolons, eg "Hei der! ; Hello there ;!;"

I know which ones I want to replace (I have their index in the string). Using replace does not work as I'm not able to use an index with it.

Strings in python are immutable, so you cannot treat them as a list and assign to indices.

Use .replace() instead:

line = line.replace(';', ':')

If you need to replace only certain semicolons, you'll need to be more specific. You could use slicing to isolate the section of the string to replace in:

line = line[:10].replace(';', ':') + line[10:]

That'll replace all semi-colons in the first 10 characters of the string.

You can do the below, to replace any char with a respective char at a given index, if you wish not to use .replace()

word = 'python'
index = 4
char = 'i'

word = word[:index] + char + word[index + 1:]
print word

o/p: pythin

Turn the string into a list; then you can change the characters individually. Then you can put it back together with .join:

s = 'a;b;c;d'
slist = list(s)
for i, c in enumerate(slist):
    if slist[i] == ';' and 0 <= i <= 3: # only replaces semicolons in the first part of the text
        slist[i] = ':'
s = ''.join(slist)
print s # prints a:b:c;d

If you want to replace a single semicolon:

for i in range(0,len(line)):
 if (line[i]==";"):
     line = line[:i] + ":" + line[i+1:]

Havent tested it though.