title: Global Variable Throws `Variable not defined` error
body: <p>I am trying to make a Ping Pong game using Python and make a scoring system to keep track of how many points each &quot;paddle&quot; or player will score. This is the code I have so far:</p>
  <pre class="lang-py prettyprint-override"><code>score = 0
  
  def point_for_paddle1():
      score = score + 1
      turtle.write(score)
  </code></pre>
  <p>When I run the code it says that the score is not defined. I believe this problem is being caused by the score = score + 1 line.</p>
  <p>How should I fix that?
  I'm fairly new to python but all types of answers are appreciated. Thanks in advance!
  P.s I'm using Python 3.</p>