updated docstring

# the main algorithm

def flip_image(img: np.ndarray):

def flip_image(img: np.ndarray) -> np.ndarray:

    """ flip an input image

    This function uses an awesome algorithm to flip an input image.

    Returns

    -------

    img_flipped: np.ndarray

        the flipped image

    """

    try:

        assert img.ndim == 2

        img_flipped = img[::-1, ::-1]

        return img_flipped

    except AssertionError:

        raise AssertionError("The input image is {}D not 2D!".format(img.ndim))

    return img[::-1, ::-1]

# a demo on how to read test image

def some_arbitrary_functions():

    """ an arbitrary function """

    return

from .flip_image import flip_image, read_test_image

from .some_other_modules import some_arbitrary_functions

__all__ = ["flip_image", "read_test_image"]

__all__ = ["flip_image", "read_test_image", "some_arbitrary_functions"]