def get_mask_file(img_file):
    """Takes an image file name and returns the corresponding mask file. The mask represents
       pixels that belong to the object. Default implentation assumes mask file has same path
       as image file with different extension only. Write custom code for getting mask file here
       if this is not the case.

    Args:
        img_file(string): Image name
    Returns:
        string: Correpsonding mask file path
    """
    return img_file.with_suffix(".pbm")