SQLAlchemy:插入语句、实际SQL和跳过字段

我有以下的sqlAlchemy模型:

class SchemaVersion(Base):
    __tablename__ = 'schema_version'

    timestamp = Column(DateTime, default=datetime.datetime.utcnow, primary_key=True)
    version   = Column(String)
    notes     = Column(String)

我能做到的最接近的是:

statement = insert(SchemaVersion).values(version='v1.0.0',
                                         notes='Initial schema')

print(statement.compile(engine, compile_kwargs={'literal_binds': True}))

engine 是我使用的引擎吗(Postgres)

生成的打印SQL是:

INSERT INTO schema_version (timestamp, version, notes) VALUES (%(timestamp)s, 'v1.0.0', 'Initial schema')

问题当然是 %(timestamp)s

我怎样才能通过 now() 作为值还是让SQLAlchemy为我使用默认值?如果我尝试:

statement = insert(SchemaVersion).values(timestamp=datetime.datetime.utcnow(),
                                         version='v1.0.0',
                                         notes='Initial schema')

我得到错误:

NotImplementedError: Don't know how to literal-quote value datetime.datetime(2018, 8, 21, 9, 50, 11, 732957)