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('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.
Answers:
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
.
SQL Alchemy also has is_
and isnot
functions you can use. An example would be
Model.filter(Model.deleted.is_(False))
@Jruv Use # noqa
in front of statement, it’ll ignore the warning.
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:
field == False
is converted to field = false
field == True
is converted to field = true
field == None
is converted to field IS NULL
-
for is_()
we get:
field.is_(False)
is converted to field IS false
field.is_(True)
is converted to field IS true
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
Why don’t you use .filter_by(field=True)
/ .filter_by(field=False)
?
caseNum = session.query(TestCase).filter(~TestCase.obsoleted).count()
print(caseNum)
works.try it in your sqlalchemy versions
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.
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
.
SQL Alchemy also has is_
and isnot
functions you can use. An example would be
Model.filter(Model.deleted.is_(False))
@Jruv Use # noqa
in front of statement, it’ll ignore the warning.
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:field == False
is converted tofield = false
field == True
is converted tofield = true
field == None
is converted tofield IS NULL
-
for
is_()
we get:field.is_(False)
is converted tofield IS false
field.is_(True)
is converted tofield IS true
field.is_(None)
is converted tofield 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
Why don’t you use .filter_by(field=True)
/ .filter_by(field=False)
?
caseNum = session.query(TestCase).filter(~TestCase.obsoleted).count()
print(caseNum)
works.try it in your sqlalchemy versions