title: Python NoneType object is not callable (beginner)
body: <p>It tells me line 1 and line 5 (new to debugging/programming, not sure if that helps)</p>
  
  <pre class="lang-py prettyprint-override"><code>def hi():
      print('hi')
  
  
  def loop(f, n):  # f repeats n times
      if n &lt;= 0:
          return
      else:
          f()
          loop(f, n-1)
  </code></pre>
  
  <pre class="lang-sh prettyprint-override"><code>&gt;&gt;&gt; loop(hi(), 5)
  hi
  f()
  TypeError: 'NoneType' object is not callable
  </code></pre>
  
  <p>Why does it give me this error?</p>