adding a character to the last string element of a list

[Peter Hansen]

Philippe C. Martin wrote:
> l = ['ABCDE','FGHI']

Okay so far...

> l[1:] #returns ['FGHI']

Which is a _copy_ (via slicing) of part of the list.  Another way of 
saying this is that it is a _new_ list which has a copy of the 
references from the appropriate part of the old list.

Try "l[1:] is l[1:]" to prove that...

> l[1:][0] #return 'FGHI'

Sure does.  From the new list.

> a = l[1:][0] + 'J' #a becomes 'FGHIJ'

Because you are actually storing a reference to the new list, whose 
first element you have modified.

> l[1:][0] += 'J' #NO ERROR BUT l[1:][0] == 'FGHI'

You are modifying the first element of the *copy* of the slice of the 
list, but you don't ever store a copy of it.  When you try to check what 
happened with the second part, you are creating yet another copy of part 
of the list and sure enough the original has never been changed.

> What am I missing ?

That slicing makes copies.  If you directly access the element in the 
first list (without using a slice) it will work.

(I think I've got most of the correct...)

-Peter