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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