Is this a bug? Variables are identical references to the same string in this example (Python)

Question

This is for Python 2.6.

I could not figure out why a and b are identical:

>>> a = "some_string"
>>> b = "some_string"
>>> a is b
True

But if there is a space in the string, they are not:

>>> a = "some string"
>>> b = "some string"
>>> a is b
False

If this is normal behavior, could someone please explain what is going on.

Edit: Disclaimer ! This is not being used to check for equality. I actually wanted to explain to someone else that "is" is only to check identity, not equality. And from the documentation I had understood that references created in this way will be different, that a new string will be created each time. The very first example I gave threw me off when I couldn't prove my own point!

Edit: I understand that this is not a bug, and interning was a new concept for me. This seems to be a good explanation.

Answer 1

Python may or may not automatically intern strings, which determines whether future instances of the string will share a reference.

If it decides to intern a string, then both will refer to the same string instance. If it doesn't, it'll create two separate strings that happen to have the same contents.

In general, you don't need to worry about whether this is happening or not; you usually want to check equality, a == b, not whether they're the same object, a is b.