title: Colon expected error
body: <p>I have a simple problem.</p>
  
  <pre><code>class MyObj:
     ...
     def get_file_name(self):
      return "myfile.txt" 
  
  some_obj = MyObj()
  
  # Error: Colon expected
  with open some_obj.get_file_name() as f:
    print("dealing with file ...")
    # do something on f
  </code></pre>
  
  <p><code>MyObj</code> class has a method called <code>get_file_name(self)</code>, which returns a string of file name.</p>
  
  <p>In the code of opening the file, I got compiler error <strong>Colon expected</strong>. I don't see where/why colon needed. Please help me why I got this error?</p>