def osr_proj(input_osr):
    """Return the projection WKT of a spatial reference object

    Args:
        input_osr (:class:`osr.SpatialReference`): the input OSR
            spatial reference

    Returns:
        WKT: :class:`osr.SpatialReference` in WKT format

    """
    return input_osr.ExportToWkt()