title: Python: Why is my `for` loop being skipped?
body: <p>I have this code:</p>
  <pre><code>for i in range(40):
      print(&quot;execution:&quot;, i, end=&quot;    &quot;)
      if player_y - i &gt;= 0:
          if roomMap[player_y - i][player_x] == 1:
              roomMap[player_y - i][player_x] = 3
  </code></pre>
  <p>The variables <code>player_x</code>, <code>player_y</code> and the list <code>roomMap</code> are already defined, but it does nothing and I am unsure what's happening.</p>