title: Python Crash Course- project 'Alien Invasion' -Error
body: <p>I started writing the code for the file name <em>alien_invasion.py</em> in the book python crash course, page number 228. I encountered the following error-
  <em>NameError: name '<em>name</em>' is not defined</em></p>
  <p>This occurs when the final lines of the program in the file <em>alien_invasion.py</em> written within the <em>if</em> block is executed. That is</p>
  <pre><code>if _name_ == '_main_':
    ai. = AlienInvasion()
    ai.run_game()
  </code></pre>