def _read_band_number(file_path):
    """
    :type file_path: Path
    :return:
    >>> _read_band_number(Path('reflectance_brdf_2.tif'))
    '2'
    >>> _read_band_number(Path('reflectance_terrain_7.tif'))
    '7'
    >>> p = Path('/tmp/something/LS8_OLITIRS_NBAR_P54_GALPGS01-002_112_079_20140126_B4.tif')
    >>> _read_band_number(p)
    '4'
    """
    number = file_path.stem.split('_')[-1].lower()

    if number.startswith('b'):
        return number[1:]

    return number