title: Default value with primary key sqlalchemy
body: <p>I've the following class</p>
  
  <pre><code>class Comision(Base):
      __tablename__ = 'comision'
  
      id = Column(Integer, primary_key=True)
      key = Column(Integer, default=process())
  </code></pre>
  
  <p>in the column key i've the def <code>process</code> and i need to make some operations with the primary key of that table, it is possible to pass it like argument?</p>