title: sqlalchemy : inserting only a part of a row
body: <p>I am new to sqlalchemy and run into a problem.
  I can't find a way to insert only a part of a new row.
  With the <code>session.add()</code> I can insert a row if I give all columns. But what if i only want to give some columns?</p>
  
  <p>On the internet, i found some places that told me to use the <code>.insert()</code></p>
  
  <pre><code>sqlalchemy.sql.expression.insert(table, values=None, inline=False, **kwargs)
  </code></pre>
  
  <p>(new to programming so I don't fully understand these lines yet)</p>
  
  <p>I imported</p>
  
  <pre><code>import sqlalchemy
  from sqlalchemy import create_engine
  from sqlalchemy.ext.declarative import declarative_base 
  from sqlalchemy import Column, Integer, String, ForeignKey, Boolean
  from sqlalchemy.orm import relationship, backref
  from sqlalchemy.orm import sessionmaker
  from sqlalchemy.sql.expression import insert
  
  Base = declarative_base()
  engine = create_engine('sqlite:///test.db')
  
  class Users(Base):
      __tablename__ = 'users'
  
      id = Column(Integer, primary_key=True)
      name = Column(String, unique=True)
      password = Column(String)
      email = Column(String)
  
      def __init__(self, name, password, email):
          self.name = name
          self.password = password
          self.email = email
  
  Session = sessionmaker(bind=engine)
  Session.configure(bind=engine)
  session = Session()
  
  session.add(users.insert().values(name="some name"))
  </code></pre>
  
  <p>Now this last line keeps giving me an AttributeError, <code>(Users has no attribute insert)</code></p>
  
  <p>What am I doing wrong?</p>