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Python | Alternate Cycling in list
• Last Updated : 05 Sep, 2019

Sometimes, while working with a Python list, we can have a problem in which we need to perform the access/printing of list in different ways. In some variations, there might be a need for printing the list in an alternate cyclic way, i.e printing elements from front and read alternatively. This is a popular problem in-school programming. Let’s discuss a certain way in which this task can be performed.

Method : Using `reversed() + islice() + iter() + cycle() + next()` + list comprehension
The combination of above functions can be employed to perform this task. In this, `reversed() and iter()` are used to create iterators of reversed and normal sequence list respectively, `cycle() `performs the task of alternate access. The `islice()` performs the task of extracting the elements and construct to new list. The` next()` performs the task of accessing elements.

Code :

 `# Python3 code to demonstrate working of``# Alternate Cycling in list``# using reversed() + islice() + iter() + cycle() + next() + list comprehension``from` `itertools ``import` `islice, cycle`` ` `# initialize list``test_list ``=` `[``5``, ``6``, ``8``, ``9``, ``10``, ``21``, ``3``]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# Alternate Cycling in list``# using reversed() + islice() + iter() + cycle() + next() + list comprehension``res ``=` `[``next``(i) ``for` `i ``in` `islice(cycle((``iter``(test_list), ``                                     ``reversed``(test_list))), ``len``(test_list))]`` ` `# printing result``print``(``"Alternate Cyclic iteration is : "` `+` `str``(res))`
Output :
```The original list is : [5, 6, 8, 9, 10, 21, 3]
Alternate Cyclic iteration is : [5, 3, 6, 21, 8, 10, 9]
```

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