Sessions in Python

A Session is a unit of work: add, flush, commit or roll back.

from sqlalchemy import create_engine
from sqlalchemy.orm import DeclarativeBase, Mapped, Session, mapped_column


class Base(DeclarativeBase):
    pass


class Run(Base):
    __tablename__ = "runs"
    id: Mapped[int] = mapped_column(primary_key=True)
    lang: Mapped[str]
    tpm: Mapped[float]


engine = create_engine("sqlite+pysqlite:///:memory:")
Base.metadata.create_all(engine)

with Session(engine) as session:
    session.add_all([Run(lang="python", tpm=104.0), Run(lang="rust", tpm=98.0)])
    session.commit()

    fetched = session.get(Run, 1)
    print(fetched.lang, fetched.tpm)
    fetched.tpm = 110.0
    session.commit()
    print(session.get(Run, 1).tpm)

How it works

1. add stages an object; commit writes and expires it.
2. Session.get fetches by primary key.
3. The context manager closes the session on the way out.

Keywords and builtins used here

• Base
• Run
• as
• class
• float
• id
• int
• pass
• print
• str
• with

The run, in numbers

Lines

27

Characters to type

625

Tokens

163

Three-star pace

110 tpm

At the three-star pace of 110 tokens a minute, this run takes about 89 seconds.

Type this snippet

Step 3 of 5 in SQLAlchemy, step 15 of 19 in Web services & data access.

← Previous Next →