flake8 complains on boolean comparison “==” in filter clause

Question

I have a boolean field in the mysql db table.

# table model
class TestCase(Base):
    __tablename__ = \'test_cases\'
    ...
    obsoleted = Column(\'obsole         


        

Answer 1

That's because SQLAlchemy filters are one of the few places where == False actually makes sense. Everywhere else you should not use it.

Add a # noqa comment to the line and be done with it.

Or you can use sqlalchemy.sql.expression.false:

from sqlalchemy.sql.expression import false

TestCase.obsoleted == false()

where false() returns the right value for your session SQL dialect. There is a matching sqlalchemy.expression.true.

Answer 2

SQL Alchemy also has is_ and isnot functions you can use. An example would be

Model.filter(Model.deleted.is_(False))

More on those here

Answer 3

@Jruv Use # noqa in front of statement, it'll ignore the warning.

Answer 4

I have a look what exact query is generated for using SQLAlchemy when == and is_ when the database dialect is Postgresql for boolean field:

• for == we get:

  1. field == False is converted to field = false
  2. field == True is converted to field = true
  3. field == None is converted to field IS NULL

• for is_() we get:

  1. field.is_(False) is converted to field IS false
  2. field.is_(True) is converted to field IS true
  3. field.is_(None) is converted to field IS NULL

NOTE: is_(not None) will be evaluated to is_(bool(not None) what gives is_(True) giving field = true so you rather go for isnot(None) producing field IS NOT NULL