from sqlalchemy import *

postgres_engine = create_engine('postgres', {'database':'prova', 
                        'host':'127.0.0.1', 
                        'user':'postgres', 
                        'password':'1234'}, 
                                 echo=False )

engine = postgres_engine

testtable = Table("test_table", engine,
    Column("id", Integer, Sequence("table_id_seq"), primary_key=True),
    Column("test_column", Integer, nullable=False),
         )

#testtable.drop()
    
class Tab(object):
    pass
    
#testtable.create()

#table.insert().execute(test_column=None)

Tab.mapper = mapper(Tab, testtable)

a=Tab()
a.test_column=4
objectstore.commit()

a.test_column=None
objectstore.commit()