title: Difference between class and instance methods
body: <p>I was reading <a href="https://pep8.org/" rel="noreferrer">PEP 8</a> (<a href="http://www.python.org/dev/peps/pep-0008/" rel="noreferrer">style guide</a>), and I noticed that it suggested to use <em>self</em> as the first argument in an instance method, but <em>cls</em> as the first argument in a class method.</p>
  <p>I've used and written a few classes, but I've never encountered a class method (well, a method which passes <em>cls</em> as a parameter). What are some examples?</p>