Lists and Tuples and Much More

[Gabriel Genellina]

En Thu, 12 Apr 2007 19:38:55 -0300, Scott <s_broscious at comcast.net>  
escribió:

> List's and Tuple's
> I don't see the distinction between the two.  I mean, I understand that a
> list is mutable and a tuple is immutable.
> The thing that I dont understand about them is what, besides that,  
> seperates
> the two.

Perhaps this old post from 2001 can explain a bit:
http://groups.google.com/group/comp.lang.python/browse_thread/thread/7eaf9fe92b4c7e47/#78e78f179a893526
Or perhaps this one from 1998:
http://groups.google.com/group/comp.lang.python/browse_thread/thread/358ef18309812fbb/14199e16f119a020

> Now you can add to a list, but not a tuple so:
>
>>>> my_list.append(my_tuple)  #or extend for that matter right?
> [1, 2, 3, 4, 5, 6, (1, 2, 3, 4, 5, 6)]
>
> Is that pretty much accurate? And which is better on resources....I'm
> guessing a tuple seeing as it doesn't change.

Yes. Tuples are immutable - once created, they can't change.

> And the last example brings up another question.  What's the deal with a
> tupple that has a list in it such as:
>
>>>> my_tupple = (1, 2, 3, 4, 5, [6, 7, 8, 9])
>
> Now I read somewhere that you could change the list inside that tupple.   
> But
> I can't find any documentation that describes HOW to do it.  The only  
> things
> I CAN find on the subject say, "Don't do it because its more trouble than
> it's worth."  But that doesn't matter to me, because I want to know
> everything.

The *contents* of the list can be changed, but not the list itself:

my_tupple[5].append(10)
del my_tupple[5][2]

my_tupple will always contain *that* list, whatever you put inside it.
(Do not confuse the list object -a container- with the objects contained  
inside it)

> Now there comes append.  I read everywhere that append only add's 1  
> element
> to the end of your list.  But if you write:
>>>> my_list = [1, 2, 3, 4, 5, 6]

my_list contains 6 elements: len(my_list)==6

>>>> my_list.append([7, 8, 9, 10])
>>>> my_list
> [1, 2, 3, 4, 5, 6, [7, 8, 9, 10]]

my_list now contains 7 elements: len(my_list)==7
Its seventh element happens to be a list itself, but that doesn't matter:  
my_list sees it as a single object like any other.

> Is that because list's, no matter what they contain, are counted as 1
> element?

Exactly. Lists or whatever object you want, if you append it to my_list,  
my_list grows by one element. It doesn't care *what* it is - it's a new  
element.

> And how would you sort the list that's in the list?  I guess that goes in
> conjunction with the section above, but still:
>>>> my_list = [6, 4, 3, 5, 2, 1]
>>>> my_list.append([7, 9, 8, 10])
>>>> my_list.sort()
>>>> my_list
> [1, 2, 3, 4, 5, 6, [7, 9, 8, 10]]

To sort my_list, you call the sort method on my_list: my_list.sort()
To sort "the list that's in the list", i.e. my_list[6], you call the sort  
method on "the list that's in the list": my_list[6].sort()

> This is, again, something I'm finding nothing on.

You call a method on any object using any_object.method_name(some,  
parameters, may_be=required)
any_object may be any arbitrary expression, like my_list[6] above

> Maybe I'm just not looking in the right spots.  The only things I have as
> learning aids are: this newsgroup ;p, http://diveintopython.org,
> http://python.org/, Beggining Python: From Novice to Professional,  and  
> (now
> don't laugh) Python for Dummies.

That's fine - just keep programming, and have fun.

-- 
Gabriel Genellina