Python Program to Alternate list elements as key-value pairs

In this article, we will learn how to get alternate list elements as key-value pairs in Python. This technique is useful when you need to transform a list into a dictionary by pairing elements at alternate positions.

Assume we have an input list containing integers. We need to create key-value pairs where each element is paired with the element that appears two positions ahead ?

Methods Used

The following are the various methods used to accomplish this task ?

• Using for loop

• Using dictionary comprehension and list slicing

Example Overview

Input

input_list = [20, 13, 5, 2, 6, 8, 18, 3]
print("Input List:", input_list)

Input List: [20, 13, 5, 2, 6, 8, 18, 3]

Expected Output

Dictionary with alternate list elements as key-value pairs:
{20: 5, 13: 2, 5: 6, 2: 8, 6: 18, 8: 3}

Each element is paired with the element two positions ahead: 20 ? 5, 13 ? 2, and so on.

Method 1: Using For Loop

This method iterates through the list and creates key-value pairs by pairing each element with the element two positions ahead ?

# input list
input_list = [20, 13, 5, 2, 6, 8, 18, 3]

# printing the given input list
print("Input List:", input_list)

# creating an empty dictionary for storing resultant dict
output_dict = {}

# traversing till the length of the input list minus 2
for i in range(len(input_list) - 2):
    # pairing current element with element at i+2 position
    output_dict[input_list[i]] = input_list[i + 2]

# printing the resultant dictionary
print("Dictionary with alternate list elements as key-value pairs:")
print(output_dict)

Input List: [20, 13, 5, 2, 6, 8, 18, 3]
Dictionary with alternate list elements as key-value pairs:
{20: 5, 13: 2, 5: 6, 2: 8, 6: 18, 8: 3}

Method 2: Using Dictionary Comprehension and List Slicing

This method uses dictionary comprehension for a more concise solution. List slicing allows us to access ranges of elements with specific step sizes ?

List Slicing Syntax

[start:stop:step]

• start ? index from where to start

• stop ? ending index (exclusive)

• step ? number of positions to skip

# input list
input_list = [20, 13, 5, 2, 6, 8, 18, 3]

# printing the given input list
print("Input List:", input_list)

# using dictionary comprehension to create key-value pairs
# pairing each element with the element two positions ahead
output_dict = {input_list[i]: input_list[i + 2] for i in range(len(input_list) - 2)}

# printing the resultant dictionary
print("Dictionary with alternate list elements as key-value pairs:")
print(output_dict)

Input List: [20, 13, 5, 2, 6, 8, 18, 3]
Dictionary with alternate list elements as key-value pairs:
{20: 5, 13: 2, 5: 6, 2: 8, 6: 18, 8: 3}

Alternative Approach: Using zip() Function

The zip() function provides another elegant solution by pairing elements from two slices of the list ?

# input list
input_list = [20, 13, 5, 2, 6, 8, 18, 3]

# printing the given input list
print("Input List:", input_list)

# using zip to pair elements
output_dict = dict(zip(input_list[:-2], input_list[2:]))

# printing the resultant dictionary
print("Dictionary with alternate list elements as key-value pairs:")
print(output_dict)

Input List: [20, 13, 5, 2, 6, 8, 18, 3]
Dictionary with alternate list elements as key-value pairs:
{20: 5, 13: 2, 5: 6, 2: 8, 6: 18, 8: 3}

Comparison

Conclusion

This article demonstrated three methods to create key-value pairs from alternate list elements. Dictionary comprehension and the zip() function provide more Pythonic solutions, while the for loop approach offers better readability for beginners.