Python 如何在 for 循环中跳过几次迭代
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How do I skip a few iterations in a for loop
提问by Alex S
In python I usually loop through ranges simply by
在python中，我通常简单地循环遍历范围
for i in range(100):
#do something
but now I want to skip a few steps in the loop. More specifically, I want something like continue(10)so that it would skip the whole loop and increase the counter by 10. If I were using a for loop in C I'd just sum 10 to i, but in Python that doesn't really work.
但现在我想跳过循环中的几个步骤。更具体地说，我想要类似的东西，continue(10)这样它就可以跳过整个循环并将计数器增加 10。如果我在 C 中使用 for 循环，我只会将 10 与 相加i，但在 Python 中这并没有真正起作用。
采纳答案by Martijn Pieters
You cannot alter the target list (iin this case) of a forloop. Use a whileloop instead:
您不能更改循环的目标列表（i在本例中）for。改用while循环：
while i < 10:
i += 1
if i == 2:
i += 3
Alternatively, use an iterable and increment that:
或者，使用可迭代和增量：
from itertools import islice
numbers = iter(range(10))
for i in numbers:
if i == 2:
next(islice(numbers, 3, 3), None) # consume 3
By assigning the result of iter()to a local variable, we can advance the loop sequence inside the loop using standard iteration tools (next(), or here, a shortened version of the itertoolsconsume recipe). fornormally calls iter()for us when looping over a iterator.
通过将 的结果分配给iter()局部变量，我们可以使用标准迭代工具（next()，或者这里是itertools消耗配方的缩短版本）推进循环内的循环序列。for通常iter()在循环迭代器时调用我们。
回答by Gareth Latty
The best way is to assign the iterator a name - it is common have an iterable as opposed to an iterator (the difference being an iterable - for example a list - starts from the beginning each time you iterate over it). In this case, just use the iter()built-in function:
最好的方法是为迭代器分配一个名称——通常有一个迭代器而不是迭代器（区别在于迭代器——例如列表——每次迭代时从头开始）。在这种情况下，只使用了iter()内置函数：
numbers = iter(range(100))
Then you can advance it inside the loop using the name. The best way to do this is with the itertoolsconsume()recipe- as it is fast (it uses itertoolsfunctions to ensure the iteration happens in low-level code, making the process of consuming the values very fast, and avoids using up memory by storing the consumed values):
然后您可以使用名称在循环内推进它。要做到这一点，最好的办法是在itertoolsconsume()配方-因为它是快（其使用itertools功能，以确保迭代发生在低级别的代码，使得速度非常快消耗值的过程，并避免使用内存的存储消耗值)：
from itertools import islice
import collections
def consume(iterator, n):
"Advance the iterator n-steps ahead. If n is none, consume entirely."
# Use functions that consume iterators at C speed.
if n is None:
# feed the entire iterator into a zero-length deque
collections.deque(iterator, maxlen=0)
else:
# advance to the empty slice starting at position n
next(islice(iterator, n, n), None)
By doing this, you can do something like:
通过这样做，您可以执行以下操作：
numbers = iter(range(100))
for i in numbers:
...
if some_check(i):
consume(numbers, 3) # Skip 3 ahead.
回答by Josh Buell
Why not just set the value to skip until? Like:
为什么不将值设置为跳过直到？喜欢：
skip_until = 0
for i in range(100):
if i < skip_until:
continue
if SOME_CONDITION:
skip_until = i + 10
DO_SOMETHING()
where SOME_CONDITION is whatever causes you to skip and DO_SOMETHING() is the actual loop contents?
其中 SOME_CONDITION 是导致您跳过的原因，而 DO_SOMETHING() 是实际的循环内容？
回答by Jonathan
for i in range(0, 100, 10):
print(i)
will print 0, 10, 20 ...
将打印 0, 10, 20 ...
