[Tutor] python's default argument value handling in functions -weird syntax? problem grappling with the concept

[Alan Gauld]

>
> My questions:
> - is the '==' operation a 'list' comparison - rather than a pointer
> comparison? (my experiments seem to indicate that it is a 'list'
> comparison)

Forget pointers and all you ever knew of them from C.
Trying to think of Python in terms of Pointers is ultimately
an excercise in frustration. Python uses dictionaries for its
indirection not memory addresses.

> - if this is the case, then why does the 'if L==[5]' test still
catch
> later on, when the 'L' should no longer be a '[5]' list?

It shouldn't! Are you absolutely sue about that? I didn't
see a case in your examples where the [5] case would fail...

> - if this is *not* the case then, then how do you determine the '=='
> is supposed to match?

It should match if both are [5]

> - or is this a matter of 'compare by value' first, then after we get
a
> match, we 'compare by reference' later on???

The actual semanics of omparisons for all Pythons types are
described in the Language reference. But mostly you can ignore
it and it will just work...

Alan G
Author of the Learn to Program web tutor
http://www.freenetpages.co.uk/hp/alan.gauld