SQLAlchemy: tablename as a variable

Question

I am working on a prototype to pull stocks ticks and dump them to a DB. I want to pass __tablename__ as a parameter to SQLAchemy so that stock ticks for a given stocks gets written down to its own table. (BTW, I am new to SQLAlchemy)

I referred this thread: Python Sqlalchemy - tablename as a variable

And came up with below code:

from sqlalchemy import create_engine from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker, scoped_session from sqlalchemy import Column, String, Integer, Date Base = declarative_base() def create_models(tablename): class Stock(Base): __tablename__ = tablename timestamp = Column(String, primary_key=True) ltp = Column(String) def __init__(self, timestamp, ltp): self.timestamp = timestamp self.ltp = ltp create_models('ABCD') engine = create_engine('sqlite:////ticks.db') Base.metadata.create_all(bind=engine) session_factory = sessionmaker(bind=engine) Session = scoped_session(session_factory)() tick = Stock('2019-02-12 09:15:00', '287') Session.merge(tick) Session.commit()

But it fails:

Traceback (most recent call last): File "quickies.py", line 32, in <module> tick = Stock('2019-02-12 09:15:00', '287') NameError: name 'Stock' is not defined

The error is quite obvious. But then I am unsure how to proceed with __tablename__ as a variable. Any pointers would be of great help.

No. I believe Base.metadata.create_all(bind=engine) this line is creating the table. If I remove the create_models function and run the code by hardcoding __tablename__, the code works fine. It creates table on 1st run and on subsequent runs, it continues to inserts the records. — slayedbylucifer
– slayedbylucifer, Commented Feb 12, 2019 at 9:03
@ChetanAmeta, If I take class Stock out side of create_models, then how do I pass __tablename__ as a variable. — slayedbylucifer
– slayedbylucifer, Commented Feb 12, 2019 at 9:06
use return Stock in your function and then Stock = create_models('ABCD') then tick = Stock('2019-02-12 09:15:00', '287') — Chetan Ameta
– Chetan Ameta, Commented Feb 12, 2019 at 9:11

Chetan Ameta · Accepted Answer · 2019-02-12 09:31:13Z

The scope of your Stock class limited to create_models function. To create object of this class outside the function you can return the class from the function and then use it.

have a look on below solution:

def create_models(tablename): class Stock(Base): __tablename__ = tablename timestamp = Column(String, primary_key=True) ltp = Column(String) def __init__(self, timestamp, ltp): self.timestamp = timestamp self.ltp = ltp return Stock #return the class Stock = create_models('ABCD') tick = Stock('2019-02-12 09:15:00', '287')

have a look at Python scope tutorial for more detail related to scope.

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