What is a function parameter =[] for?

[Chris Angelico]

On Fri, Nov 20, 2015 at 5:50 AM, BartC <bc at freeuk.com> wrote:
> But you're not going to tell me what it is I got wrong!
>
> I said that Python's "=" does a very shallow copy. And I stated that in A=B,
> something of B must be copied into A.
>
> I (and probably others) would like to know why none of that is correct. But
> I suspect I'm not wrong.

There's no copying happening. You evaluate the expression `B`, and get
back some kind of object (because all expressions in Python evaluate
to objects, unless they raise exceptions or in some way don't finish
evaluating). The name A then becomes bound to that object. You're not
copying a reference; you're simply referencing the result of an
expression.

PLEASE finish reading Ned's talk. Here's the link again:

http://nedbatchelder.com/text/names1.html

It is an excellent explanation of the exact points you're confused about.

ChrisA