Python Code Example: Flattening a Nested List

Flattening a nested list involves converting a list of lists into a single list containing all the elements from the nested lists. This can be useful in various data processing tasks where a simplified, single-level list is required. There are different ways to achieve this in Python, including using recursion or list comprehensions. Here, we’ll demonstrate a recursive approach to flatten a nested list.

Code Example

def flatten(nested_list):
    # Initialize an empty list to store the flattened elements
    flattened_list = []

    # Recursive function to process each element in the nested list
    def flatten_element(element):
        # If the element is a list, recursively flatten it
        if isinstance(element, list):
            for item in element:
                flatten_element(item)
        else:
            # If the element is not a list, append it to the flattened list
            flattened_list.append(element)

    # Start flattening from the top level of the nested list
    flatten_element(nested_list)
    
    return flattened_list

# Example usage
nested_list = [1, [2, 3], [4, [5, 6]], 7]
flattened_list = flatten(nested_list)
print(f"Flattened list: {flattened_list}")

Code Explanation

Defining the flatten Function

The flatten function is defined to take a nested list as an argument. It initializes an empty list flattened_list to store the flattened elements.

def flatten(nested_list):
    flattened_list = []

Recursive Helper Function

A nested helper function flatten_element is defined within flatten to process each element in the nested list. This function uses recursion to handle elements that are lists themselves.

def flatten_element(element):
    if isinstance(element, list):
        for item in element:
            flatten_element(item)
    else:
        flattened_list.append(element)

• Checking if Element is a List: The function checks if the current element is a list using isinstance(element, list). If it is, the function iterates over each item in the list and recursively calls flatten_element on it.
• Appending Non-list Elements: If the element is not a list, it is appended to the flattened_list.

Flattening the Top Level

The flatten_element function is initially called with the top-level nested_list. This starts the recursion process to flatten all nested lists.

flatten_element(nested_list)
return flattened_list

Example Usage

An example nested list is defined and passed to the flatten function. The resulting flattened list is printed.

nested_list = [1, [2, 3], [4, [5, 6]], 7]
flattened_list = flatten(nested_list)
print(f"Flattened list: {flattened_list}")