Python: Inject a number in between each pair of adjacent numbers in a list of numbers

Last update on May 30 2025 11:50:16 (UTC/GMT +8 hours)

Inject Separator Between Numbers

Given a list of numbers and a number to inject, write a Python program to create a list containing that number in between each pair of adjacent numbers.

Input: [12, -7, 3, -89, 14, 88, -78, -1, 2, 7]
Separator: 6
Output:
[12, 6, -7, 6, 3, 6, -89, 6, 14, 6, 88, 6, -78, 6, -1, 6, 2, 6, 7]

Input: [1, 2, 3, 4, 5, 6]
Separator: 9
Output:
[1, 9, 2, 9, 3, 9, 4, 9, 5, 9, 6]

Visual Presentation:

Sample Solution-1:

Python Code:

# License: https://bit.ly/3oLErEI

# Define a function named 'test' that takes a list of numbers and a separator as input
def test(nums, sep):
    # Initialize a list 'ans' with double the length of 'nums' minus one, filled with separators
    ans = [sep] * (2 * len(nums) - 1)
    
    # Replace every second element of 'ans' with the corresponding elements from 'nums'
    ans[::2] = nums
    
    return ans  # Return the modified list

# Example 1
nums1 = [12, -7, 3, -89, 14, 88, -78, -1, 2, 7]
separator1 = 6
print("List of numbers:", nums1)
print("Separator:", separator1)
print("Inject the separator in between each pair of adjacent numbers of the said list:")
print(test(nums1, separator1))

# Example 2
nums2 = [1, 2, 3, 4, 5, 6]
separator2 = 9
print("\nList of numbers:", nums2)
print("Separator:", separator2)
print("Inject the separator in between each pair of adjacent numbers of the said list:")
print(test(nums2, separator2))

Sample Output:

List of numbers: [12, -7, 3, -89, 14, 88, -78, -1, 2, 7]
Separator: 6
Inject the separator in between each pair of adjacent numbers of the said list:
[12, 6, -7, 6, 3, 6, -89, 6, 14, 6, 88, 6, -78, 6, -1, 6, 2, 6, 7]

List of numbers: [1, 2, 3, 4, 5, 6]
Separator: 9
Inject the separator in between each pair of adjacent numbers of the said list:
[1, 9, 2, 9, 3, 9, 4, 9, 5, 9, 6]

Flowchart:

Sample Solution-2:

Python Code:

# License: https://bit.ly/3oLErEI

# Define a function named 'test' that takes a list of numbers and a separator as input
def test(nums, sep):
    result = []  # Initialize an empty list to store the result
    
    # Iterate through the indices of 'nums'
    for i in range(len(nums)):
        # Check if the current index is the last one
        if i == len(nums) - 1:
            result.append(nums[i])  # If it is the last index, append the number without the separator
        else:
            result.append(nums[i])  # Append the current number to the result
            result.append(sep)      # Append the separator after the current number
    
    return result  # Return the modified list

# Example 1
nums1 = [12, -7, 3, -89, 14, 88, -78, -1, 2, 7]
separator1 = 6
print("List of numbers:", nums1)
print("Separator:", separator1)
print("Inject the separator in between each pair of adjacent numbers of the said list:")
print(test(nums1, separator1))

# Example 2
nums2 = [1, 2, 3, 4, 5, 6]
separator2 = 9
print("\nList of numbers:", nums2)
print("Separator:", separator2)
print("Inject the separator in between each pair of adjacent numbers of the said list:")
print(test(nums2, separator2))

Sample Output:

List of numbers: [12, -7, 3, -89, 14, 88, -78, -1, 2, 7]
Separator: 6
Inject the separator in between each pair of adjacent numbers of the said list:
[12, 6, -7, 6, 3, 6, -89, 6, 14, 6, 88, 6, -78, 6, -1, 6, 2, 6, 7]

List of numbers: [1, 2, 3, 4, 5, 6]
Separator: 9
Inject the separator in between each pair of adjacent numbers of the said list:
[1, 9, 2, 9, 3, 9, 4, 9, 5, 9, 6]

For more Practice: Solve these Related Problems:

• Write a Python program to insert a given separator between every two adjacent numbers in a list using slicing.
• Write a Python program to interleave a separator into a list of integers using list comprehension.
• Write a Python program to create a new list with a specified value inserted between each pair of elements from the input list.
• Write a Python program to implement a function that merges a list and a separator element into a new interleaved list.

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