Python imports - Are these executable statements run?

Question

I took a look at the tutorial here: http://www.pythoncentral.io/introductory-tutorial-python-sqlalchemy/

The decisive parts for my question are first:

import os
import sys
from sqlalchemy import Column, ForeignKey, Integer, String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
from sqlalchemy import create_engine

Base = declarative_base()

class Person(Base):
    __tablename__ = 'person'
    # Here we define columns for the table person
    # Notice that each column is also a normal Python instance attribute.
    id = Column(Integer, primary_key=True)
    name = Column(String(250), nullable=False)

class Address(Base):
    __tablename__ = 'address'
    # Here we define columns for the table address.
    # Notice that each column is also a normal Python instance attribute.
    id = Column(Integer, primary_key=True)
    street_name = Column(String(250))
    street_number = Column(String(250))
    post_code = Column(String(250), nullable=False)
    person_id = Column(Integer, ForeignKey('person.id'))
    person = relationship(Person)

# Create an engine that stores data in the local directory's
# sqlalchemy_example.db file.
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)

and second:

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

from sqlalchemy_declarative import Address, Base, Person

engine = create_engine('sqlite:///sqlalchemy_example.db')
# Bind the engine to the metadata of the Base class so that the
# declaratives can be accessed through a DBSession instance
Base.metadata.bind = engine

DBSession = sessionmaker(bind=engine)
# A DBSession() instance establishes all conversations with the database
# and represents a "staging zone" for all the objects loaded into the
# database session object. Any change made against the objects in the
# session won't be persisted into the database until you call
# session.commit(). If you're not happy about the changes, you can
# revert all of them back to the last commit by calling
# session.rollback()
session = DBSession()

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

# Insert an Address in the address table
new_address = Address(post_code='00000', person=new_person)
session.add(new_address)
session.commit()

If the second part is run (e.g. "python second_part"), won't the import statement

from sqlalchemy_declarative import Address, Base, Person

cause all executable code in the first part to run? (Which would trigger the code which creates tables in a db each time the first part is run)

Best regards

Answer 1

Yes, every time, the first file is imported, the tables are created again.

To prevent this, use the following statements:

if __name__ == '__main__':
    Base.metadata.create_all(engine)