How to reverse tuples in Python?

python loops iteration tuples
Joan Venge picture Joan Venge · Apr 18, 2012 · Viewed 79.7k times · Source

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.

Answer

tobyodavies picture tobyodavies · Apr 18, 2012

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!

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