title: Replacing one character of a string in python
body: <p>In python, are strings mutable?  The line <code>someString[3] = "a"</code> throws the error </p>
  
  <blockquote>
    <p>TypeError: 'str' object does not
    support item assignment</p>
  </blockquote>
  
  <p>I can see why (as I could have written someString[3] = "test" and that would obviously be illegal) but is there a method to do this in python?</p>