title: TypeError: unsupported operand type(s) for -=: 'str' and 'int'
body: <p>I have to make a countdown using the while loop where you pick a number and the code will do a countdown to 0: this is what I've done:</p>
  
  <pre><code>chosen_number = 0
  chosen_number = raw_input('Choose a number: ')
  while chosen_number &gt; 0:
      print chosen_number
      chosen_number -= 1
  </code></pre>
  
  <p>But it gives me a syntax error in the last line:</p>
  
  <pre><code>TypeError: unsupported operand type(s) for -=: 'str' and 'int'
  </code></pre>
  
  <p>What causes this syntax error?</p>