title: member or class variables in python
body: <p>I come from Java, so I'm getting confused here.</p>
  
  <pre><code>class Sample(object):
      x = 100                     # class var?
      def __init__(self, value):
          self.y = value          # instance var?
          z = 300                 # private var? how do we access this outside Sample?
  </code></pre>
  
  <p>What is the difference between the 3 variable declarations?</p>