timmy wrote:
> i make a copy of a list, and delete an item from it and it deletes it
> from the orginal as well, what the hell is going on?!?!?!
>
> #create the staff copy of the roster
> Roster2 = []
> for ShiftLine in Roster:
> #delete phone number from staff copy
> Roster2.append(ShiftLine)
> del Roster2[len(Roster2)-1][1]
>
> Roster2 should have nothing to do with Roster, right??? doing a print of
> both lists confirms that the phone number has been removed from both
>
First of all, you could have said
del Roster2[-1][1]
since negative indices count backwards from the end of the list. This
has nothing to do with your problem, though.
Fredrik has already given you a correct, somewhat condensed, answer. Let
me elaborate. I guess that Roster is a list of lists. Then actually, it
is a list of references to lists (really a reference to a list of
references to lists). Your for-loop makes Roster2 a shallow copy of
Roster, i.e. Roster2 is a new list with references to the _same_
sublists as in Roster. So, Roster2[-1] references the same object as
Roster[-1], not a copy of it. To get copies, you could change your
.append-line to
Roster2.append(ShiftLine[:])
which gives you shallow copies of the sublists. If there are mutables in
the sublists, you may still get into trouble. In that case, maybe you
should take a look at copy.deepcopy.
HTH
/MiO
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