Help with extracting characters from string

[DeaD_EyE]

I separated the task in two subtasks.

First Task: Generator to generate indices
Second Task: Join the text. The indices from the generator are used to get the characters.

def index_gen(end):
    """
    GeneratorFunction for indicies

    The generator yield numbers from 0 to < end.
    Example:
    
    >>> list(index_gen(20))
    [0, 1, 3, 6, 10, 15]
    """
    
    current = 0
    step = 1
    
    while current < end:
        yield current
        current += step
        step += 1


def task(text):
    """
    >>> text = "A clown has a red nose."
    >>> task(text)
    'A lnsee'
    """
    return "".join(text[idx] for idx in index_gen(len(text)))


if __name__ == "__main__":
    # Input string: "A clown has a red nose.".
    # Output string: "A lnsee".
    text = "A clown has a red nose."

    print(text)
    print(task(text))