The challenge then becomes when variables are shared within multiple threads, how CPython locks the reference count. There is a “global interpreter lock” that carefully controls thread execution. The interpreter can only execute one operation at a time, regardless of how many threads it has.
When CPython creates variables, it allocates the memory and then counts how many references to that variable exist, this is a concept known as reference counting. If the number of references is 0, then it frees that piece of memory from the system. This is why creating a “temporary” variable within say, the scope of a for loop, doesn’t blow up the memory consumption of your application.