In article <11**********************@22g2000hsm.googlegroups. com>,
Shafik <sh******@gmail.comwrote:
Hello folks,
I am an experienced programmer, but very new to python (2 days). I
wanted to ask: what exactly is the difference between a tuple and a
list? I'm sure there are some, but I can't seem to find a situation
where I can use one but not the other.
Lists and tuples are both sequences, and can be used interchangeably in
many situations. The big difference is that lists are mutable (can be
modified), and tuples are immutable (cannot be modified). Lists also
have a richer API (for example the index and count methods).
If you are going to need to change the contents of the sequence
(appending, removing, altering a value, etc), then use a list.
If you require the sequence to be immutable (such as being used as the
key in a dictionary), then use a tuple.
In general, tuples should be a little more efficient than lists.
However, altering a list is more efficient than creating a new tuple, so
"always prefer tuples" does not necessarily lead to a faster overall
program. Unless performance is critical, I wouldn't worry about this
factor.
IMHO, a more important reason to prefer tuples is that since they are
immutable, you don't have to worry about side effects. If you call a
function and pass it a list, you have no guarantee that the list won't
be changed during the function call. With tuples, any attempt to change
the tuple will raise an exception. If it is important to the caller
that the sequence remain unchanged, then a tuple is a safer
representation for that sequence.
Dave
