In Base class add onupdate in the last statement as follows:
from sqlalchemy.sql import func
last_time = Column(TIMESTAMP, server_default=func.now(), onupdate=func.current_timestamp())
In Base class add onupdate in the last statement as follows:
from sqlalchemy.sql import func
last_time = Column(TIMESTAMP, server_default=func.now(), onupdate=func.current_timestamp())