title: call function use .apply in python
body: <p>I have a shortcode as following. try to use <code>.apply</code> to call a function. but it always gives me the error saying the function is not callable.</p>
  
  <pre><code>def awesome_count():
      return 10
  products['awesome'] = products['word_count'].apply(awesome_count())
  </code></pre>
  
  <hr>
  
  <pre><code>AssertionError Traceback (most recent call last)
  &lt;ipython-input-45-493b4bfe94cc&gt; in &lt;module&gt;()
  ----&gt; 1 products['awesome'] = products['word_count'].apply(awesome_count())
  
  C:\Users\twu\AppData\Local\Dato\Dato Launcher\lib\site-packages\graphlab\data_structures\sarray.pyc in apply(self, fn, dtype, skip_undefined, seed)
     1598         [0.0, 1.0, 2.0]
     1599         """
  -&gt; 1600         assert callable(fn), "Input function must be callable."
     1601 
     1602         dryrun = [fn(i) for i in self.head(100) if i is not None]
  
  AssertionError: Input function must be callable.
  </code></pre>
  
  <p>Can somebody help me out?</p>