title: Given a subset of attributes on a class instance, increment one randomly
body: <p>I have a Python class as such:</p>
  
  <pre><code>class Zoo:
    pandas = 0
    tunas = 0
    cows = 0
  
    #...other attributes and methods below
  </code></pre>
  
  <p>Because of divine forces outside of my control, I <strong>cannot modify the class in any way whatsoever</strong> (yes, I realize a dictionary of animals would be better here). I would like to write code which will operate on an instance of the class, and increment a random attribute amongst the 3 shown above by 1.</p>
  
  <p>In essence, I'd like to write something like this:</p>
  
  <pre><code>import random
  z = Zoo()
  attributes = [z.pandas, z.tunas, z.cows]
  random.choice(attributes) += 1
  </code></pre>
  
  <p>Of course, this doesn't work. How would one go about doing this?</p>