title: How to name class variables
body: <p>Is there a convention on how class variables should be named (as different from instance variables), or is there no real difference. For example:</p>
  
  <pre><code>import pymysql
  
  class DB:
      NUM_CONNECTIONS = 0
      def __init__(self):
          self.conn = None
          self.cursor = None
      def __repr__(self):
          return 'Closed connection' if not self.conn else f'Open conection @ 0x{id(self):x}'
      def connect(self):
          if self.conn: return
          self.conn = pymysql.connect(host='127.0.0.1',user='root')
          self.cursor = self.conn.cursor()
          DB.NUM_CONNECTIONS += 1
  </code></pre>
  
  <p>Currently I usually do variables as <code>CLASS_VARIABLES</code> and <code>instance_variables</code>. What are some common patterns for this?</p>