def strof(o):
    """``o`` can be either a string or bytes or other object convertible to
    string. In case of bytes, it will be decoded using 'utf-8'. In case of
    None, None will be returned."""
    if isinstance(o, str):
        return o
    elif isinstance(o, bytes):
        return o.decode('utf-8')
    elif o == None:
        return None
    else:
        return str(o)
