如何在Python中反转元组？ [英] How to reverse tuples in Python?

问题描述

可能重复：

在Python中以相反的顺序遍历列表

这可能吗？没有必要到位，只是想找到一种方法来反转一个元组，这样我就可以向后迭代它。

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.

推荐答案

有两种惯用的方法：

reversed(x)  # returns an iterator

或

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

由于元组是不可变的，所以无法反转元组就地。

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

编辑：
建立@ lvc的评论， 反转返回的迭代器相当于

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]

ie它依赖于具有已知长度的序列，以避免必须实际反转元组。

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

至于哪个更有效，我怀疑它是 seq [:: - 1] 如果您使用全部且元组很小，并且元组的反转很大，但是在python中的性能通常是令人惊讶的，所以测量它！

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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