Flattens a nested list of arbitrary depth into a flat list.

flatten_list.py

def flatten(lst):
    """
    Flattens a nested list of arbitrary depth into a flat list.

    This function recursively traverses each element in a list. If an element is a list,
    it is further flattened. This continues until no nested lists remain, producing a
    flat list containing all non-list elements from the original nested structure.

    Parameters:
    - lst (list): The list to be flattened. Can contain nested lists of arbitrary depth.

    Returns:
    - generator: A generator yielding elements of the flattened list.

    Examples:
    >>> list(flatten([1, [2, 3], [4, [5, 6, [7, 8]], 9], 10]))
    [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

    >>> list(flatten([[1, 2], [3, [4, 5]], 6]))
    [1, 2, 3, 4, 5, 6]

    >>> list(flatten(['a', ['b', 'c', ['d']], 'e']))
    ['a', 'b', 'c', 'd', 'e']
    """
    for item in lst:
        if isinstance(item, list):
            yield from flatten(item)  # If the item is a list, recurse
        else:
            yield item  # If the item is not a list, yield it directly