I can assume that you have model of this table, you should add there new update method like this:
class table(Base):
__tablename__ = 'table'
id = Column(Integer, primary_key=True)
available = Column(DateTime)
asd = Column(Unicode(255))
def update(self, available=None, asd = None): #etc.
if available:
self.available = available
if asd:
self.asd = asd
and updating happens then like this:
import transaction
with transaction.manager:
t=session.query(Table).filter(Table.id==1).first() #search the object what you want to update
t.update(available=datetime.now()) #you can update only one or several cell like this