Python Coding challenge - Day 622| What is the output of the following Python Code?

 

Code Explanation:

1. Define the function flatten_once(lst)

def flatten_once(lst):

This function is a generator that flattens a list only one level deep.

2. Loop over the list elements

for sub in lst:

Iterates over each item in the list lst.

For the input:

[1, [2, 3], 4]

The elements in order are:

1 (not a list)

[2, 3] (a list)

4 (not a list)

3. Check if element is a list

if isinstance(sub, list):

If the current element is a list, we want to yield its items individually.

4. Yield items based on type

If it's a list:

yield from sub

For [2, 3], this means yield 2, then 3.

If it's not a list:

yield sub

For 1 and 4, they are yielded directly.

How it Processes the Input

Given:

flatten_once([1, [2, 3], 4])

The generator yields:

1 → from yield sub

2 → from yield from [2, 3]

3 → from yield from [2, 3]

4 → from yield sub

Final Output

[1, 2, 3, 4]

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