Actualizar un elemento en SQLAlchemy - Python

Tutorial | Aprender Python
import datetime

from sqlalchemy import Column
from sqlalchemy import ForeignKey
from sqlalchemy import Integer, DateTime
from sqlalchemy import String
from sqlalchemy.orm import declarative_base
from sqlalchemy.orm import relationship
from sqlalchemy.sql import func

Base = declarative_base()

class User(Base):
    __tablename__ = "user"
    id = Column(Integer, primary_key=True)
    name = Column(String(30),unique=True,default="")
    fullname = Column(String(200), default="")
    value = Column(Integer, default=0)
    time_created = Column(DateTime(timezone=True), server_default=func.now())
    time_updated = Column(DateTime(timezone=True), onupdate=func.now())

    def __repr__(self):
        return f"User(id={self.id!r}, name={self.name!r}, fullname={self.fullname!r})"


# Connection
from sqlalchemy import create_engine

engine = create_engine("postgresql+psycopg2://scott:tiger@localhost:5432/mydatabase")

# Insertar
with Session(engine) as session:
        c = User(
            name="juan",
            fullname="perez",
        )
        session.add_all([c])
        session.commit()

# Actualizar
with Session(engine) as session:
    # stmt = select(User).where(User.name == "juan")
    # r = session.execute(stmt).first()["User"]
    r = session.query(User).filter(User.name == "juan").first()
    print(r.value)
    r.value += 2
    print(r.value)
    session.commit()
Referencias

Tutorial | Aprender Python