def get_conv_fname(fname: str, dest_ext: str, output_dir=None) -> str:
    """Returns the filename and path of the file after conversion

    Arguments:
    fname -- the original filename
    dest_ext -- the extension of the destination file
    output_dir -- the output directory of the operation
    """

    if output_dir is not None:
        fname_wo_path = fname.split('/')[-1][:-4] + '.' + dest_ext
        if output_dir[-1] != '/':
            output_dir = output_dir + '/'
        return output_dir + fname_wo_path
    else:
        return fname[:-4] + '.' + dest_ext