flake8 complains on boolean comparison "==" in filter clause

python mysql sqlalchemy flake8
Jruv picture Jruv · Sep 25, 2013 · Viewed 19.4k times · Source

I have a boolean field in the mysql db table. 

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

To get the count of all the non-obsoleted test cases, that can be done simply like this:

caseNum = session.query(TestCase).filter(TestCase.obsoleted == False).count()
print(caseNum)

That works fine, but the flake8 report the following warning:

E712: Comparison to False should be "if cond is False:" or "if not cond:"

Okay, I think that make sense. So change my code to this:

caseNum = session.query(TestCase).filter(TestCase.obsoleted is False).count()

or 

caseNum = session.query(TestCase).filter(not TestCase.obsoleted).count()

But neither of them can work. The result is always 0. I think the filter clause doesn't support the operator "is" or "is not". Will someone can tell me how to handle this situation. I don't want to disable the flake.

Answer

Martijn Pieters picture Martijn Pieters · Sep 25, 2013

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.

Related questions

ImportError: No module named MySQLdb

I am referring the following tutorial to make a login page for my web application. http://code.tutsplus.com/tutorials/intro-to-flask-signing-in-and-out--net-29982 I am having issue with the database. I am getting an ImportError: No module named MySQLdb when I execute …

Read More
Bulk insert with SQLAlchemy ORM

Is there any way to get SQLAlchemy to do a bulk insert rather than inserting each individual object. i.e., doing: INSERT INTO `foo` (`bar`) VALUES (1), (2), (3) rather than: INSERT INTO `foo` (`bar`) VALUES (1) INSERT INTO `foo` (`bar`) VALUES (2) INSERT INTO `…

Read More
How do I get a raw, compiled SQL query from a SQLAlchemy expression?

I have a SQLAlchemy query object and want to get the text of the compiled SQL statement, with all its parameters bound (e.g. no %s or other variables waiting to be bound by the statement compiler or MySQLdb dialect …

Read More