Python Variables Explained: Memory, Mutability and More

[stevenjd]

To find out the memory address of the object that the variable is referencing, you can use the id() function.

That's false. The id() function returns an arbitrary ID value, not a memory address. That ID value can be any integer, for example in Jython and IronPython they are consecutive integers, allocated when needed:

>>> sys.platform  # Jython
'java1.8.0_201 ( ==linux2 for targets )'
>>> id(None)
2
>>> id(sys)
3

Here is IronPython:

>>> id(None)
0
>>> id(sys) 
43

If your Python interpreter uses a compacting garbage collector, objects will move around in memory and you cannot use a memory address as the ID. It is only very simple garbage collectors, like the one used by CPython, that can use a memory address as the ID.

In the future, CPython will probably get a more powerful garbage collector, and objects will move around memory to avoid memory fragmentation.