How to use the sqlalchemy.DateTime function in SQLAlchemy

log = logging.getLogger(__name__)
log.setLevel(logging.DEBUG)
handler = logging.StreamHandler(sys.stdout)
format = "%(name)s %(levelname)s %(asctime)s %(message)s"
formatter = logging.Formatter(format)
handler.setFormatter(formatter)
log.addHandler(handler)

now = datetime.datetime.utcnow

metadata = MetaData()

SkipToolTest_table = Table("skip_tool_test", metadata,
                           Column("id", Integer, primary_key=True),
                           Column("create_time", DateTime, default=now),
                           Column("update_time", DateTime, default=now, onupdate=now),
                           Column("repository_metadata_id", Integer, ForeignKey("repository_metadata.id"), index=True),
                           Column("initial_changeset_revision", TrimmedString(255), index=True),
                           Column("comment", TEXT))


def upgrade(migrate_engine):
    print(__doc__)
    metadata.bind = migrate_engine
    metadata.reflect()
    # Initialize.
    if migrate_engine.name == 'mysql' or migrate_engine.name == 'sqlite':
        default_false = "0"
    elif migrate_engine.name in ['postgresql', 'postgres']:
        default_false = "false"

def upgrade():
    ### commands auto generated by Alembic - please adjust! ###
    op.add_column('rss_parser_funcs', sa.Column('last_changed', sa.DateTime(), nullable=True))
    op.add_column('rss_parser_funcs_version', sa.Column('last_changed', sa.DateTime(), autoincrement=False, nullable=True))


    bind = op.get_bind()
    sess = Session(bind=bind)

    print("Updating date/time stamps for functions.")
    sess.query(RssFeedEntry).update({'last_changed' : datetime.datetime.now()})
    sess.commit()
    print("Update done.")

    op.alter_column('rss_parser_funcs', 'last_changed', nullable=False)

def is_datetime_field(col):
    """
    Check if a column is DateTime (or implements DateTime)

    :param Column col: the column object to be checked

    :rtype: bool
    """
    if hasattr(col.type, "impl"):
        return type(col.type.impl) is DateTime
    else:
        return type(col.type) is DateTime

def downgrade():
    op.drop_constraint(None, 'pystock_currency')
    op.drop_column(u'pystock_fxrates', sa.Column('created_on', sa.DateTime(), nullable=True))
    op.drop_table('pystock_book')
    op.drop_table('pystock_user')
    op.drop_table('pystock_exchange')
    op.drop_table('pystock_liability')
    op.drop_table('pystock_company')

def upgrade(migrate_engine):
    # Upgrade operations go here. Don't create your own engine;
    # bind migrate_engine to your metadata
    meta = MetaData()
    meta.bind = migrate_engine

    placement_groups = Table(
        'placement_groups', meta,
        Column('id', Integer, primary_key=True, nullable=False),
        Column('pgid', String(length=255), nullable=False),
        Column('state', String(length=255), nullable=False),
        Column('up', String(length=255), nullable=False),
        Column('acting', String(length=255), nullable=False),
        Column('created_at', DateTime(timezone=False)),
        Column('updated_at', DateTime(timezone=False)),
        Column('deleted_at', DateTime(timezone=False)),
        Column('deleted', Boolean(create_constraint=True, name=None)),
    )

    try:
        placement_groups.create()
    except Exception:
        meta.drop_all(tables=[placement_groups])
        raise

raw_body = Column(Text, nullable=True, default=None)
	url = Column(Text, nullable=True, default=None)
	
	author = Column(String, nullable=True, default=None)
	domain = Column(String, nullable=True, default=None)
	
	score = Column(Integer, nullable=True, default=None)
	num_comments = Column(Integer, default=0)
	
	# Comma-separated list of child ids
	# Currently not used, saving those in case we'll need comment ranking info later on
	child_ids = Column(Text)
	
	# Date fields
	date_posted = Column(DateTime, default=datetime.utcnow)
	date_updated = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
	date_entered_fp = Column(DateTime, default=None)
	date_left_fp = Column(DateTime, default=None)
	
	deleted = Column(Integer, default=0)
	dead = Column(Integer, default=0)
	
	# PostgreSQL search fields
	title_tsv = Column(TSVECTOR)
	body_tsv = Column(TSVECTOR)
	
	
	
	# def update

def upgrade():
    op.create_table(
        'bazeltarget',
        sa.Column('id', sa.GUID(), nullable=False),
        sa.Column('step_id', sa.GUID(), nullable=False),
        sa.Column('job_id', sa.GUID(), nullable=False),
        sa.Column('name', sa.Text(), nullable=False),
        sa.Column('status', sa.Enum(), nullable=False),
        sa.Column('result', sa.Enum(), nullable=False),
        sa.Column('duration', sa.Integer(), nullable=True),
        sa.Column('date_created', sa.DateTime(), nullable=False),
        sa.ForeignKeyConstraint(
            ['step_id'], ['jobstep.id'], ondelete='CASCADE'),
        sa.ForeignKeyConstraint(
            ['job_id'], ['job.id'], ondelete='CASCADE'),
        sa.PrimaryKeyConstraint('id')
    )

def __init__(self, md5=None):
        self.md5 = md5
        self.count = 0

    def __repr__(self):
        return '<img>' % (self.id, self.md5)


class Score(Base):
    __tablename__ = 'scores'
    id = Column(Integer, primary_key=True)
    user = Column(Integer)
    image = Column(Integer)
    score = Column(Integer)
    ts = Column(DateTime)
    nouce = Column(Integer)

    def __init__(self, user, image, score=0):
        self.user = user
        self.image = image
        self.score = score
        self.ts = datetime.utcnow()
        self.nouce = random.randint(0, 10000)

    def __repr__(self):
        return '%d, %d&gt;' % (self.user, self.image, self.score)


@login_manager.user_loader
def load_user(user_id):
    return db_session.query(User).filter(User.id == int(user_id)).one_or_none()

def upgrade():
    '''
    upgrade method
    '''
    create_table('lifetime_except',
                 sa.Column('id', GUID()),
                 sa.Column('scope', sa.String(25)),
                 sa.Column('name', sa.String(255)),
                 sa.Column('did_type', DIDType.db_type(name='LIFETIME_EXCEPT_DID_TYPE_CHK')),
                 sa.Column('account', sa.String(25)),
                 sa.Column('comments', sa.String(4000)),
                 sa.Column('pattern', sa.String(255)),
                 sa.Column('state', LifetimeExceptionsState.db_type(name='LIFETIME_EXCEPT_STATE_CHK')),
                 sa.Column('updated_at', sa.DateTime),
                 sa.Column('expires_at', sa.DateTime),
                 sa.Column('created_at', sa.DateTime))

    if context.get_context().dialect.name != 'sqlite':
        create_primary_key('LIFETIME_EXCEPT_PK', 'lifetime_except', ['id', 'scope', 'name', 'did_type', 'account'])
        create_check_constraint('LIFETIME_EXCEPT_SCOPE_NN', 'lifetime_except', 'scope is not null')
        create_check_constraint('LIFETIME_EXCEPT_NAME_NN', 'lifetime_except', 'name is not null')
        create_check_constraint('LIFETIME_EXCEPT_DID_TYPE_NN', 'lifetime_except', 'did_type is not null')

def upgrade():
    ### commands auto generated by Alembic - please adjust! ###
    op.add_column('nu_outbound_wrappers', sa.Column('released_on', sa.DateTime(), nullable=True))
    ### end Alembic commands ###