One way to categorize type systems is by whether they are nominal or structural:

• in a nominal system, comparison between types are based on names and declarations; The Python type system is mostly nominal, where an int can be used in place of a float because of their subtype relationship.
• in a structural system, comparisons between types are based on structure. You could define a structural type Sized that includes all instances that define .__len__(), irrespective of their nominal type.

References

• https://realpython.com/python-type-checking/#type-theory
• subtypes
• types