Python: Flatten a given nested list structure

Python List: Exercise - 72 with Solution

Write a Python program to flatten a given nested list structure.

Sample Solution-1:

Python Code:

def flatten_list(n_list):
    result_list = []
    if not n_list: return result_list
    stack = [list(n_list)]
    while stack:
        c_num = stack.pop()
        next = c_num.pop()
        if c_num: stack.append(c_num)
        if isinstance(next, list):
            if next: stack.append(list(next))
        else: result_list.append(next)
    result_list.reverse()
    return result_list 
n_list = [0, 10, [20, 30], 40, 50, [60, 70, 80], [90, 100, 110, 120]]
print("Original list:") 
print(n_list)
print("\nFlatten list:")
print(flatten_list(n_list))

Sample Output:

Original list:
[0, 10, [20, 30], 40, 50, [60, 70, 80], [90, 100, 110, 120]]

Flatten list:
[0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120]

Flowchart:

Visualize Python code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

Sample Solution-2:

Loop over elements, use list.extend() if the element is a list, list.append() otherwise.

Python Code:

def flatten_list(nums):
  result = []
  for i in nums:
    result.extend(i) if isinstance(i, list) else result.append(i)
  return result     
n_list = [0, 10, [20, 30], 40, 50, [60, 70, 80], [90, 100, 110, 120]]
print("Original list:") 
print(n_list)
print("\nFlatten list:")
print(flatten_list(n_list))

Sample Output:

Original list:
[0, 10, [20, 30], 40, 50, [60, 70, 80], [90, 100, 110, 120]]

Flatten list:
[0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120]

Flowchart:

Visualize Python code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

Python Code Editor:

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous: Write a Python program to check whether all dictionaries in a list are empty or not.
Next: Write a Python program to remove consecutive (following each other continuously) duplicates (elements) of a given list.