What happens when you assign the value of one variable to another variable in Python?
This is my second day of learning python (I know the basics of C++ and some OOP.), and I have some slight confusion regarding variables in python.
Here is how I understand them currently:
Python variables are references (or pointers?) to objects (which are either mutable or immutable). When we have something like
num = 5, the immutable object
5 is created somewhere in memory, and the name-object reference pair
num is created in a certain namespace. When we have
a = num, nothing is being copied, but now both variables refer to the same object and
a is added to the same namespace.
This is where my book, Automate the boring stuff with Python , confuses me. As it's a newbie book, it doesn't mention objects, namespaces, etc., and it attempts to explain the following code:
>>> spam = 42 >>> cheese = spam >>> spam = 100 >>> spam 100 >>> cheese 42
The explanation it offers is exactly the same as that of a C++ book, which I am not happy about as we are dealing with references/pointers to objects. So in this case, I guess that in the 3rd line, as integers are immutable,
spam is being assigned an entirely new pointer/reference to a different location in memory, i.e. the memory that it was initially pointing to wasn't modified. Hence we have
cheese referring to the initial object referred to by
spam. Is this the correct explanation?
As a C++ developer you can think of Python variables as pointers.
Thus when you write
spam = 100, this means that you "assign the pointer", which was previously pointing to the object
42, to point to the object
cheese was assigned to point to the same object as
spam pointed to, which happened to be
42 at that time. Since you have not modified
cheese, it still points to
Immutability has nothing to do with it in this case, since pointer assignment does not change anything about the object being pointed to.