Python Identity operators with variables and datastructures

Question

I have the following code:

a = []
b = a

when I compile the following code I get this:

print(b is a) --> True
print(b is []) --> False

if b = a then shouldn't b is [] return True?

`is` means referential equality, so that both things refer to the *same* object, two separate lists are *not* the same object. — Willem Van Onsem, Jul 31 '19 at 21:46
Whether a literal produces a new object or refers to an existing object is basically an implementation detail. Don't use `is` with literals. — chepner, Jul 31 '19 at 21:47
I should say, for *immutable* values it is an implementation detail. For mutable values, caching a value will cause problems. — chepner, Jul 31 '19 at 21:48
Not all `[]` are the same object. `[]` is just an empty list, which can be constructed in many ways. — hpaulj, Jul 31 '19 at 22:12

score 5 · Accepted Answer · answered Jul 31 '19 at 21:46

5

try that:

    a = []
b = a


print(id(a))
print(id(b))
print(id([]))

And you will see that a and b refers to the same object, while next [] is a different one. Check if b to see if b is not empty list

answered Jul 31 '19 at 21:46

snamef

1 Answers1