What happens when you assign the value of one variable to another variable in Python?

Question

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 unde

Answer 1

The way I see it there are different views of a language.

• The "language lawyer" perspective.
• The "practical programmer" perspective.
• the "implementor" perspective.

From the language lawyer perspective python variables always "point at" an object. However unlike Java and C++ the behvaiour of == <= >= etc depends on the runtime type of the objects that the variables point at. Furthermore in python memory management is handled by the language.

From a practical programmer perspective we can treat the fact that integers, strings, tuples etc are immutable* objects rather than straight values as an irrelevent detail. The exception is when storing large ammounts of numeric data we may want to use types that can store the values directly (e.g. numpy arrays) rather than types that will end up with an array full of references to tiny objects.

From an implementers perspective most languages have some sort of as-if rule such that if the specified behaviours are correct the implementation is correct regardless of how things are actually done under the hood.

So yes your explanation is correct from a language lawyer perspective. Your book is correct from a practical programmer perspective. What an implementation actually does depends on the implementation. In cpython integers are real objects though small value integers are taken from a cache pool rather than created anew. I'm not sure what the other implementations (e.g. pypy and jython) do.

* note the distinction between mutable and immutable objects here. With a mutable object we have to be careful about treating it "like a value" because some other code might mutate it. With an immutable object we have no such concerns.