Proper autogenerate of __str__() implementation also for sqlalchemy classes?

Question

I would like to display / print my sqlalchemy classes nice and clean.

In Is there a way to auto generate a __str__() implementation in python? the answer You can it

Answer 1

I define this __repr__ method on my base model:

def __repr__(self):
    fmt = '{}.{}({})'
    package = self.__class__.__module__
    class_ = self.__class__.__name__
    attrs = sorted((col.name, getattr(self, col.name)) for col in self.__table__.columns)
    sattrs = ', '.join('{}={!r}'.format(*x) for x in attrs)
    return fmt.format(package, class_, sattrs)

The method displays the names of all of a table's columns (but not relationships), and the repr of their values, in alphabetical order. I don't usually define a __str__ unless I need a particular form - perhaps str(User(name='Alice')) would just be Alice - so str(model_instance) will call the __repr__ method.

Sample code

import datetime

import sqlalchemy as sa
from sqlalchemy.ext import declarative


class BaseModel(object):

    __abstract__ = True

    def __repr__(self):
        fmt = u'{}.{}({})'
        package = self.__class__.__module__
        class_ = self.__class__.__name__
        attrs = sorted((c.name, getattr(self, c.name)) for c in self.__table__.columns)
        sattrs = u', '.join('{}={!r}'.format(*x) for x in attrs)
        return fmt.format(package, class_, sattrs)


Base = declarative.declarative_base(cls=BaseModel)


class MyModel(Base):

    __tablename__ = 'mytable'

    foo = sa.Column(sa.Unicode(32))
    bar = sa.Column(sa.Integer, primary_key=True)
    baz = sa.Column(sa.DateTime)

>>> mm = models.MyModel(foo='Foo', bar=42, baz=datetime.datetime.now())
>>> mm
models.MyModel(bar=42, baz=datetime.datetime(2019, 1, 4, 7, 37, 59, 350432), foo='Foo')