title: Replacing instances of a character in a string
body: <p>This simple code that simply tries to replace semicolons (at i-specified postions) by colons does not work:</p>
  
  <pre><code>for i in range(0,len(line)):
       if (line[i]==";" and i in rightindexarray):
           line[i]=":"
  </code></pre>
  
  <p>It gives the error </p>
  
  <pre><code>line[i]=":"
  TypeError: 'str' object does not support item assignment
  </code></pre>
  
  <p>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.</p>
  
  <p><strong>Example</strong></p>
  
  <p>In the string I might have any number of semicolons, eg "Hei der! ; Hello there ;!;"</p>
  
  <p>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.</p>