DEV Community

Shahrouz Nikseresht
Shahrouz Nikseresht

Posted on

Day 30: Python List Merger, Combine Two Lists Manually with Loops

#python #challenge #beginners #programming

Welcome to Day 30 of the #80DaysOfChallenges journey! This beginner challenge is about merging two lists into one without built-in operators, relying on loops to append elements one by one. It reinforces list basics, iteration, and manual construction, key for understanding data structures before shortcuts. If you're solidifying loop skills or exploring how lists grow, this "Python merge lists" exercise demonstrates a function that's simple yet illustrative of step-by-step building, easy to modify for interleaving or filtering.

💡 Key Takeaways from Day 30: List Merge Function

This task creates a function that takes two lists, builds a new one by appending from each, and returns it. It's a direct approach to concatenation: init empty, loop add from first, then second. We'll cover the fundamentals: function with new list init, separate loops for appending, and example with output.

1. Function Design: Empty List Start

The merge_lists function accepts two lists and returns a combined new one. Its signature is straightforward:

def merge_lists(list_1, list_2):
    """
    Return a new list that contains all elements from list_1 followed by all elements from list_2.
    """
Enter fullscreen mode Exit fullscreen mode

Begin with:

merged = []
Enter fullscreen mode Exit fullscreen mode

This creates a fresh list, avoiding mutation of inputs. The function keeps it pure, no side effects, making it reliable for chaining or reuse in larger code like data prep scripts.

2. Looping Appends: Add from Each List

Fill it sequentially:

# Add elements from the first list
for item in list_1:
    merged.append(item)

# Add elements from the second list
for item in list_2:
    merged.append(item)
Enter fullscreen mode Exit fullscreen mode

Each for loop iterates and appends, mimicking concatenation. It's explicit, great for learning how lists expand, and handles any iterable types. This method shines when you need control, like adding conditions or transformations mid-loop.

3. Return and Example: Test the Merge

Wrap with return:

return merged
Enter fullscreen mode Exit fullscreen mode

Demo it:

list_a = [1, 3, 5, 7]
list_b = [2, 4, 6, 8]

print(f"\nMerged list: {merge_lists(list_a, list_b)}\n")
Enter fullscreen mode Exit fullscreen mode

For these, it yields [1, 3, 5, 7, 2, 4, 6, 8]. The print shows the result clearly. It's a basic test, but you could add edge cases like empties or mixed types to verify robustness.

🎯 Summary and Reflections

This list merger emphasizes manual iteration over shortcuts, building a deeper grasp of lists. It drove home for me:

  • Loop utility: Separate fors keep it clear and modular.
  • Append mechanics: Shows how lists dynamically grow.
  • No mutations: New list preserves originals.

The value lies in its teachability, a stepping stone to zip or extend. For twists, try alternating elements or merging sorted.

Advanced Alternatives: Use list.extend for efficiency, or comprehensions: [item for item in list_1] + [item for item in list_2]. How do you merge collections? Share in comments!

🚀 Next Steps and Resources

Day 30 wrapped basics with list ops, setting for more structure play. In #80DaysOfChallenges? Merged differently? Post your code!

Top comments (0)