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8.11: Objects and Values

If we execute these assignment statements:

a = 'banana'
b = 'banana'

we know that a and b both refer to a string, but we don't know whether they refer to the same string. There are two possible states:

 

Variables and Objects

Variables and Objects

In one case, a and b refer to two different objects that have the same value. In the second case, they refer to the same object.

 

To check whether two variables refer to the same object, you can use the is operator.

>>> a = 'banana'
>>> b = 'banana'
>>> a is b
True

In this example, Python only created one string object, and both a and b refer to it.

But when you create two lists, you get two objects:

>>> a = [1, 2, 3]
>>> b = [1, 2, 3]
>>> a is b
False

In this case we would say that the two lists are equivalent, because they have the same elements, but not identical, because they are not the same object. If two objects are identical, they are also equivalent, but if they are equivalent, they are not necessarily identical.

 

Until now, we have been using "object" and "value" interchangeably, but it is more precise to say that an object has a value. If you execute a = [1,2,3]a refers to a list object whose value is a particular sequence of elements. If another list has the same elements, we would say it has the same value.