sqlalchemy orm - get table definition from DB - sqlalchemy

Question

SQLAlchemy, Is there a way to create table definition class directly, beacause the table has already existed in DB, most documents tell me to make the definition mannually.
Base = declarative_base()
# ORM defininition
class Dep(Base):
__tablename__='dep'
id=Column(Integer,primary_key=True,autoincrement=True)
dname=Column(String(64),nullable=False,index=True)
# Add new obs
session = sessionMaker()
row_obj=Dep(dname='saleman')
session.add(row_obj)

Answer 1

There are several of ways to reflect tables in SQLAlchemy.
I'll put here examples inspired by the documentation.
1. Giving the class an autoloaded __table__
from sqlalchemy import Table, create_engine
from sqlalchemy.orm import declarative_base
Base = declarative_base() # same declarative_base() as usual
engine = create_engine("sqlite:///mydatabase.db") # get your engine
class User(Base):
__table__ = Table("user", Base.metadata, autoload_with=engine)
2. Retrieving classes with the Automap extension
from sqlalchemy import create_engine
from sqlalchemy.ext.automap import automap_base
Base = automap_base() # rather than declarative_base()
engine = create_engine("sqlite:///mydatabase.db") # get your engine
Base.prepare(autoload_with=engine) # reflect the tables and classes
User = Base.classes.user # retrieve classes from table name
3. Inheriting from the DeferredReflection extension
from sqlalchemy.ext.declarative import DeferredReflection
from sqlalchemy.orm import declarative_base
Base = declarative_base() # same declarative_base() as usual
class User(DeferredReflection, Base): # define your class
__tablename__ = "user"
engine = create_engine("sqlite:///mydatabase.db") # get your engine
User.prepare(engine) # reflect the table and attributes
The two first examples need an engine to create the class, which can be inconvenient for testing and such, so I prefer the third one which allows me to have class and engine defined in different places, but all three will work.