sqlalchemy_nullable.py

from __future__ import print_function

from sqlalchemy import create_engine, Column, types
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, scoped_session
from sqlalchemy.orm import Session

from sqlalchemy import ForeignKey
from sqlalchemy.orm import relationship, backref

engine = create_engine('sqlite:///:memory:', echo=True)
Base = declarative_base()

session = scoped_session(sessionmaker(bind=engine))

class User(Base):
    __tablename__ = "users"
    id = Column(types.Integer, primary_key=True)
    nullable_true = Column(types.String(255), nullable=True)
    nullable_false = Column(types.String(255), nullable=False)
    nullable_default = Column(types.String(255))


Base.metadata.create_all(engine)