# Python | Combine two lists alternately

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Examples :

`  Input:  lst1 = [1, 2, 3] lst2 = [’a’,’ b’, ’c ’]  Output:  [1,’ a’, 2, ’b’, 3,’ c’]  Input:  lst1 = [’name’,’ alice’, ’bob’] lst2 = [’ marks’, 87, 56]  Output:  [’name’,’ marks’, ’alice’, 87,’ bob’, 56] `

Method # 1: List Comprehension

 ` # Python3 program for combining two lists ` ` # alternatively ` ` def ` ` countList (lst1, lst2): ` ` return ` ` [sub [item] ` ` for ` ` item ` ` in ` ` range ` ` (` ` len ` ` (lst2)) ` ` ` ` for ` ` sub ` ` in ` ` [lst1, lst2]] ` ` # Driver code ` ` lst1 ` ` = ` ` [` ` 1 ` `, ` ` 2 ` `, ` ` 3 ` `] ` ` lst2 ` ` = ` ` [` ` ’a’ ` `, ` ` ’b’ ` `, ` `’ c’ ` `] ` ` print ` ` (countList (lst1, lst2)) `

Exit:

` [1, ’a’, 2,’ b’, 3, ’c’] `

There is an alternative to using list comprehension with zip (), as follows —

Method # 2: Using `itertools.cycle()`

 ` def ` ` countList (lst1, lst2): ` ` return ` ` [item ` ` for ` ` pair ` ` in ` ` zip ` ` (lst1, lst2 ` ` + ` ` [` ` 0 ` `]) ` ` for ` ` item ` ` in ` ` pair] `
 ` # Python3 program to combine two lists ` ` # alternatively ` ` from ` ` itertools ` ` import ` ` cycle ` ` def ` ` countList (lst1, lst2) : ` ` iters ` ` = ` ` [` ` iter ` ` (lst1), ` ` iter ` ` (lst2)] ` ` return ` ` l ist ` ` (` ` iter ` ` .__ next __ () ` ` for ` ` iter ` ` in ` ` cycle (iters)) ` ` # Driver code ` ` lst1 ` ` = ` ` [` ` 1 ` `, ` ` 2 ` `, ` ` 3 ` `] ` ` lst2 ` ` = ` ` [` ` ’a’ ` `, ` `’ b ’` `, ` `’ c’ ` `] ` ` print ` ` (countList (lst1, lst2)) `

Exit:

` [1, ’a’, 2,’ b’, 3, ’c’] `

Method # 3: Using `reduce()`

` `

` # Python3 program to combine two lists # alternatively import operator from functools import reduce def countList (lst1, lst2): return reduce (operator.add, zip (lst1, lst2)) # Driver code lst1 = [ 1 , 2 , 3 ] lst2 = [ ’a’ , ’ b’ , ’c’ ] print (countList (lst1, lst2)) `

` ` Exit:

` (1, ’a’, 2,’ b’, 3, ’c’) `

Method # 4: Using the `numpy`

` `

` # Python3 program to combine two lists # alternatively import numpy as np def countList (lst1, lst2): return np.array ([[i, j] for i, j in zip (lst1, lst2)]). ravel () # Driver code lst1 = [ 1 , 2 , 3 ] lst2 = [ ’a’ , ’ b ’ , ’ c’ ] print (countList (lst1, lst2)) `

` ` Exit :

` [’1’’ a’ ’2’’ b’’ 3’’ c’] `

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We hope this article has helped you to resolve the problem. Apart from Python | Combine two lists alternately, check other array Python module-related topics.

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Javier Krasiko

Rome | 2023-02-07

Maybe there are another answers? What Python | Combine two lists alternately exactly means?. I just hope that will not emerge anymore

Davies Schteiner

Milan | 2023-02-07

Thanks for explaining! I was stuck with Python | Combine two lists alternately for some hours, finally got it done 🤗. I just hope that will not emerge anymore

Cornwall Nickolson

Boston | 2023-02-07

I was preparing for my coding interview, thanks for clarifying this - Python | Combine two lists alternately in Python is not the simplest one. Will use it in my bachelor thesis

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