title: The TypeError in python
body: <p>I'm trying to make a challenge for one of the courses I'm following. I'm new to programming, but I'm eager to learn.
  Can you tell me in detail why this error occurs to me and how do solve it.</p>
  
  <pre><code>default_names =['Justin', 'john','Emilee', 'jim','Ron','Sandra','veronica','Wiskley']
  i=0
  for i in default_names:
      default_names[i]=default_names[i][0].upper()
      i+=1
      if i==len(default_names):
          break
  
  print default_names
  </code></pre>
  
  <p>the error: <strong>TypeError: list indices must be integers, not str</strong></p>