title: Python: print multi-lines when using format string
body: <p>When I try to print multi-lines with format string in python, the bash show the error like that:</p>
  
  <pre><code>a = 'tony'
  b = '20'
  print ("I am %s\n"+
         "I am %s years old\n"
         % (a,b))
  </code></pre>
  
  <p>TypeError: not all arguments converted during string formatting</p>
  
  <p>I'm wondering what's wrong with that and what's the right way to use format string to print multi-lines.</p>
  
  <hr>
  
  <p>if i write code like this, it'll output correctly. However, the single line code will be too long, that's not what I want.</p>
  
  <pre><code>print ("I am %s\nI am %s years old\n" % (a,b))
  </code></pre>