uselist –

A boolean that indicates if this property should be loaded as a list or a scalar. In most cases, this value is determined automatically by relationship() at mapper configuration time, based on the type and direction of the relationship - one to many forms a list, many to one forms a scalar, many to many is a list. If a scalar is desired where normally a list would be present, such as a bi-directional one-to-one relationship, set relationship.uselist to False.

The relationship.uselist flag is also available on an existing relationship() construct as a read-only attribute, which can be used to determine if this relationship() deals with collections or scalar attributes:

>>> User.addresses.property.uselist
True