可以访问索引/枚举的Python列表理解吗?

consider the following Python code with which I add in a new list2 all the items with indices from 1 to 3 of list1:

请考虑下面的Python代码，我使用这些代码添加了一个新的清单2，其中列出了清单1中从1到3的所有索引项:

for ind, obj in enumerate(list1):
    if 4> ind > 0: list2.append(obj)

how would you write this using python list comprehension, if I have no access to the indices through enumerate?

如果我无法通过enumerate访问索引，那么如何使用python列表理解编写这个索引呢?

something like:

喜欢的东西:

list2 = [x for x in list1 if 4>ind>0]

but since I have no 'ind' number, would this work? :

但是既然我没有ind编号，这个可以吗?:

list2 = [x for x in enumerate(list1) if 4>ind>0]

3 个解决方案

#1

118

list2 = [x for ind, x in enumerate(list1) if 4 > ind > 0]

#2

If you use enumerate, you do have access to the index:

如果使用enumerate，你确实可以访问索引:

list2 = [x for ind, x in enumerate(list1) if 4>ind>0]

#3

Unless your real use case is more complicated, you should just use a list slice as suggested by @wim

除非您的实际用例更复杂，否则应该使用@wim建议的列表切片

>>> list1 = ['zero', 'one', 'two', 'three', 'four', 'five', 'six']
>>> [x for ind, x in enumerate(list1) if 4 > ind > 0]
['one', 'two', 'three']
>>> list1[1:4]
['one', 'two', 'three']

For more complicated cases - if you don't actually need the index - it's clearer to iterate over a slice or an islice

对于更复杂的情况(如果您实际上不需要索引)，则可以在片或islice上进行迭代

list2 = [x*2 for x in list1[1:4]]

或

from itertools import islice
list2 = [x*2 for x in islice(list1, 1, 4)]

For small slices, the simple list1[1:4]. If the slices can get quite large it may be better to use an islice to avoid copying the memory

对于小片，简单的列表1[1:4]。如果切片可以变得非常大，那么最好使用islice来避免复制内存

#1

118

list2 = [x for ind, x in enumerate(list1) if 4 > ind > 0]

#2