The Python Apprentice

Exploring value vs. identity with id()

Let's dig a little deeper into the relationship between objects and references using the built-in id() function. id() accepts any object as an argument and returns an integer identifier which is unique and constant for the lifetime of the object. Let's re-run the previous experiment using id():

>>> a = 496>>> id(a)4302202064>>> b = 1729>>> id(b)4298456016>>> b = a>>> id(b)4302202064>>> id(a) == id(b)True

Here we see that initially a and b refer to different objects and, thus, id() gives us different values for each variable. However, when we then assign a to b, both names refer to the same object so id() gives the same value for both. The main lesson here is that id() can be used to establish the identity ...