Data as relation between objects in Python

Question

Chapter Data Model in the section of Language Reference of Python documentation says:

All data in a Python program is represented by objects or by relations between objects.

I understand the part that all data in Python program is represented by objects. But what data is represented by relations between objects?

Can someone give an example with explanations, please?

Answer 1

But what data is represented by relations between objects?

For example, in

d = {2: 'b'}

the relationship is that the object 2 is mapped to the object 'b' in the dictionary d.

In

l = [2, 'b']

the relationship is that the objects 2 and b are the 0 and 1 members of the list l.

In

class Foo(object):
    def __init__(self, x):
        self._x = x

f = Foo(2)

the relationship is that the object 2 is the member _x of f.