title: Understanding "Too many ancestors" from pylint
body: <p>example.py:</p>
  
  <pre><code>'''
  demo too many ancestors 
  '''
  from flask_security.forms import RegisterForm
  from wtforms.fields import TextField
  
  class ExtendedRegisterForm(RegisterForm):
      '''An extended register form'''
      name = TextField('Name', [])
  </code></pre>
  
  <p>When I run pylint:</p>
  
  <pre><code>$ pylint -r n example.py
  ************* Module example
  R:  7, 0: Too many ancestors (10/7) (too-many-ancestors)
  </code></pre>
  
  <p>What does this mean and how can I fix it?</p>