问如何识别使用pydal使用sqlalchemy创建的sqlite数据库？

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from sqlalchemy import Column, Integer, String                                                                                                                                           
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine

from sqlalchemy.orm import sessionmaker

Base = declarative_base()

class Person(Base): 
    __tablename__ = 'person'
    id = Column(Integer, primary_key=True)
    name = Column(String(250), nullable=False)

engine = create_engine('sqlite:///sqlalchemy_example.db')

# Create all tables in the engine. This is equivalent to "Create Table"
# statements in raw SQL.
Base.metadata.create_all(engine)

Base.metadata.bind = engine

DBSession = sessionmaker(bind=engine)
session = DBSession()

# Insert a Person in the person table
new_person = Person(name='new person')
session.add(new_person)
session.commit()

from pydal import DAL, Field
db = DAL('sqlite://sqlalchemy_example.db', auto_import=True)
db.tables
>> []
db.define_table('person', Field('name'))
>> OperationalError: table "person" already exists