How to reverse tuples in Python?

> Possible Duplicate:
> Traverse a list in reverse order in Python

Is this possible? Doesn't have to be in place, just looking for a way to reverse a tuple so I can iterate on it backwards.

There are two idiomatic ways to do this:

reversed(x)  # returns an iterator

or

x[::-1]  # returns a new tuple

Since tuples are immutable, there is no way to reverse a tuple in-place.

---

Edit: Building on @lvc's comment, the iterator returned by reversed would be equivalent to

def myreversed(seq):
    for i in range(len(x) - 1, -1, -1):
        yield seq[i]

i.e. it relies on the sequence having a known length to avoid having to actually reverse the tuple.

As to which is more efficient, i'd suspect it'd be the seq[::-1] if you are using all of it and the tuple is small, and reversed when the tuple is large, but performance in python is often surprising so measure it!

You can use the reversed builtin function.

>>> x = (1, 2, 3, 4)
>>> x = tuple(reversed(x))
>>> x
(4, 3, 2, 1)

If you just want to iterate over the tuple, you can just use the iterator returned by reversed directly without converting it into a tuple again.

>>> for k in reversed(x):
...     print(k)
... 
4 3 2 1

Similar to the way you would reverse a list, i.e. s[::-1]

In [20]: s = (1, 2, 3)

In [21]: s[::-1]
Out[21]: (3, 2, 1)

and

In [24]: for i in s[::-1]:
   ....:     print i
   ....:
3
2
1