title: Python - allowed values of a variable
body: <p>How can I explicitly define what values can given variable have? Let's say I want value of variable <strong>size</strong> to be either <strong>'small'</strong>, <strong>'medium'</strong>, or <strong>'big'</strong> and nothing else.</p>
  
  <p>EDIT:
  I want to avoid a situation when variable is set to something from beyond the list (for example to 'tiny' in this case). Like enum in Java. This variable would be a class field.</p>