pass by reference - Passing values in Python

When you pass a collection like list, array to another function in python, does it make a copy of it, or is it just a pointer?

Answer

Python passes references-to-objects by value.

Python passes references-to-objects by
value (like Java), and everything in
Python is an object. This sounds
simple, but then you will notice that
some data types seem to exhibit
pass-by-value characteristics, while
others seem to act like

pass-by-reference... what's the deal?

It is important to understand mutable
and immutable objects. Some objects,
like strings, tuples, and numbers, are
immutable. Altering them inside a
function/method will create a new
instance and the original instance
outside the function/method is not
changed. Other objects, like lists

and dictionaries are mutable, which
means you can change the object
in-place. Therefore, altering an
object inside a function/method will
also change the original object
outside.