[英]python: iterate a specific range in a list
Lets say I have a list:假设我有一个清单:
listOfStuff =([a,b], [c,d], [e,f], [f,g])
What I want to do is to iterate through the middle 2 components in a way similar to the following code:我想要做的是以类似于以下代码的方式遍历中间的 2 个组件:
for item in listOfStuff(range(2,3))
print item
The end result should be as below:最终结果应如下所示:
[c,d]
[e,f]
This code currently does not work, but I hope you can understand what I am trying to do.这段代码目前不起作用,但我希望你能理解我在做什么。
listOfStuff =([a,b], [c,d], [e,f], [f,g])
for item in listOfStuff[1:3]:
print item
You have to iterate over a slice of your tuple.您必须遍历元组的一部分。 The
1
is the first element you need and 3
(actually 2+1) is the first element you don't need. 1
是您需要的第一个元素,而3
(实际上是 2+1)是您不需要的第一个元素。
Elements in a list are numerated from 0:列表中的元素从 0 开始编号:
listOfStuff =([a,b], [c,d], [e,f], [f,g])
0 1 2 3
[1:3]
takes elements 1 and 2. [1:3]
采用元素 1 和 2。
A more memory efficient way to iterate over a slice of a list would be to use islice()
from the itertools
module:迭代列表切片的一种更内存有效的方法是使用
itertools
模块中的islice()
:
from itertools import islice
listOfStuff = (['a','b'], ['c','d'], ['e','f'], ['g','h'])
for item in islice(listOfStuff, 1, 3):
print(item)
# ['c', 'd']
# ['e', 'f']
However, this can be relatively inefficient in terms of performance if the start value of the range is a large value since islice
would have to iterate over the first start value-1 items before returning items.然而,如果范围的起始值是一个大值,这在性能方面可能相对低效,因为
islice
在返回项目之前必须迭代第一个起始值 - 1 的项目。
You want to use slicing.你想使用切片。
for item in listOfStuff[1:3]:
print item
By using iter
builtin:通过使用
iter
内置:
l = [1, 2, 3]
# i is the first item.
i = iter(l)
next(i)
for d in i:
print(d)
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