You ask, "is a being destroyed and recreated as a new object?" This question is imprecise in a way that reflects your confusion. Do you mean "a", the name, or do you mean the object that "a" points to?

"a" is a name that points to an object. When you use assignment, like foo=bar or a = "blah", you are telling Python which object the name "a" should point to. In this case, a new string object with value "blah". So in your example, the name "a" is now pointing to a new object. (The old one may or may not have been "destroyed"; that doesn't matter for now.)

There are different kinds of objects. Some of them are mutable, some are immutable. Lists are mutable: a = []; a.append(3). Notice how we didn't use assignment, yet the value of the object that "a" pointed to changed. Whereas, if "a" points to a string or int, you have to use assignment to change the value of the object "a" points to.

Re-reading the above, it's kind of confusing. Let me try again.

You have cardboard boxes, and post-it notes. The post-it notes each have a variable name on them, like "a" or "foo". The boxes are objects, like ints, strings, lists, classes, dicts, anything.

When you use assignment (foo=bar), you're taking a post-it note, and sticking it on a box. Note that you can have multiple post-it notes on a box (a = b = [1,2,3]), but a post-it note (name) can't be on more than one box. Some boxes can be opened, like lists, so you can throw stuff in or take stuff out. Some boxes are locked (ok, they are transparent, lockable cardboard boxes), so you can't change what's in them. Those are called immutable.

Going back to your question, was the old value of "a" destroyed? Can the interpreter throw the box into the incinerator? It depends whether there are other post-it notes on it. (I.e., references to the object.)

Use the built-in function id to help develop your understanding. Call it from the shell on any variable or value you can get your hands on.