add default value in sqlalchemy query code example

Example 1: sqlalchemy function for default value for column

def mydefault(context):
    return context.get_current_parameters()['counter'] + 12

t = Table('mytable', meta,
    Column('counter', Integer),
    Column('counter_plus_twelve', Integer, default=mydefault, onupdate=mydefault)
)

Example 2: sqlalchemy function for default value for column

# a function which counts upwards
i = 0
def mydefault():
    global i
    i += 1
    return i

t = Table("mytable", meta,
    Column('id', Integer, primary_key=True, default=mydefault),
)