title: Upper method doesn't make sense
body: <p><strong>Code</strong>:</p>
  
  <pre><code>def solve_the_input(port):
      port = hex(int(port))
      split_result = port.split("0x")
      split_port = split_result[1]
      print 'input port is ',split_port
      split_port.upper()
      print 'input port is ',split_port
      return split_port
  
  if __name__ == "__main__":
      if len(sys.argv) == 1:
          print "please input a port"
      else:
          port = solve_the_input(sys.argv[1])
  </code></pre>
  
  <p><strong>Input</strong></p>
  
  <pre><code>python test.py 42328
  </code></pre>
  
  <p><strong>Actual Output</strong>:</p>
  
  <pre><code>input port is  a558
  input port is  a558
  </code></pre>
  
  <p><strong>Expected Output</strong>:</p>
  
  <pre><code>input port is  a558
  input port is  A558
  </code></pre>
  
  <p>I don't know why the upper() method is not working as expected.</p>