如何在 Python 中反转元组？

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最佳答案

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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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

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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