Or even print("STRING", var, "STRING")

keep in mind that for long strings, each `+` creates a new string object (at least, it did in the 2.x days and I assume it hasn't changed)

It has indeed not changed. But practically speaking it doesn't matter much. The string implementation cheats by using resizable buffers internally for at least some purposes, while presenting an immutable-type interface. But regardless, a given line of code is going to have O(1) such additions; it's not remotely as bad as `for i in items: str += foo(i)`. (This should be done using `''.join` instead.)

#Takes around 1 second s="a"*3000000000

#instant, does not consume twice as much memory. s+="a"

I don't know the internals, but certainly there's not a new string being created. Maybe if it exceeds capacity? Who cares at that point, it's python strings, not Matmuls in C.