[Tutor] creating pop method for stack class

[Christopher Spears]

> 
> First, a tip:
> 
> Instead of lista[:len(lista)-1], you can (and should) just
> write lista[:-1].
> 
> Now, what if we wrap that in a function:
> 
> >>> def shorten(lst):
> ...   lst = lst[:-1]  # identical to: lst =
> lst[:len(lst)-1]
> ...
> 
> Then test it:
> 
> >>> lista = [1, 2, 3, 4]
> >>> shorten(lista)
> 
> What do you think will be the result of:
> 
> >>> print lista
> 
> ?
> 

I see what you mean.  I have tested it, and I have gotten a weird result:
>>> def shorten(lst):
...     lst = lst[:-1]
...
>>> lista = [1,2,3,4]
>>> shorten(lista)
>>> print lista
[1, 2, 3, 4]
>>> lista = [1,2,3,4]
>>> lista = lista[:-1]
>>> print lista
[1, 2, 3]
>>>

Strange...why does it work outside of the function but not in it?  Let me try something else:

>>> def shorten(lst):
...     lst = lst[:-1]
...     return lst
...
>>> lista = [1,2,3,4]
>>> shorten(lista)
[1, 2, 3]
>>> print lista
[1, 2, 3, 4]
>>> lista = shorten(lista)
>>> print lista
[1, 2, 3]
>>>

Huh, how do you explain that?