Flatten a single-level list of lists

Summary

Flatten only one level of nesting: turn a list of lists (and/or tuples and scalars) into a single list of elements.

Problem statement

Write a function flatten_once(nested) that accepts a list which may contain other lists or tuples as elements and returns a new list with exactly one level of flattening applied. For each element in the input list: - If the element is a list or tuple, extend the output with its elements (one level deep). - Otherwise, append the element as-is. Do not perform deep flattening: if an inner element contains nested lists beyond the first level, leave those nested structures intact as elements.

Task

Implement a function that flattens one level of nesting for a list containing sublists/tuples and other elements.

Examples

Input format

A single Python list which may contain lists, tuples, or other objects as elements.

Output format

A list with one level of flattening applied.

Constraints

Only flatten one level. Preserve the order of elements. Result must be a list.

Samples