Comparison to singleton
None should be expr is None 79 )
80 max = (
81 db.session.query(func.sum(Ticket.quantity.label('sum')))
82 .filter(Ticket.event_id == obj_id, Ticket.deleted_at == None) 83 .scalar()
84 )
85 result = {
Description
Comparisons to the singleton objects, like True, False, and None, should be done with identity, not equality. Use is or is not.
Identity checks are faster than equality checks.
Also, the equality checks can result in unintended behaviour in some cases:
>>> 1 is True
False
>>> 1 == True
True
>>> 1.0 is True
False
>>> 1.0 == True
True
Bad practice
value = fx()
if value == True: # `==` can cause unintended behaviour
print(value)
if value != None:
print(value)
Recommended
value = fx()
if value is True: # `is` for Identity comparison
print(value)
if value is not None:
print(value)
Exceptions:
Equality comparisons might be required in some cases, especially in SQLAlchemy, SQLObject, ORMs, etc. In these cases, it is safe to ignore this issue.