Best reference that I know of: "Traits: A Mechanism for Fine-grained Reuse" by:
OSCAR NIERSTRASZ and NATHANAEL SCHARLI
ANDREW P. BLACK
Inheritance is well-known and accepted as a mechanism for reuse in object-oriented languages. Unfortunately, due to the coarse granularity of inheritance, it may be difficult to decompose an application into an optimal class hierarchy that maximizes software reuse. Existing schemes based on single inheritance, multiple inheritance, or mixins, all pose numerous problems for reuse. To overcome these problems we propose traits, pure units of reuse consisting only of methods. We develop a formal model of traits that establishes how traits can be composed, either to form other traits, or to form classes. We also outline an experimental validation in which we apply traits to refactor a non-trivial application into composable units.
Note that there are several packages already in PyPI:
(Never used them myself).