def isnpdot(val):
    """
    check if the entry starts with 'np.'

    Parameters
    ----------
    val: str
        a string entry

    Returns
    -------
    bool
        True if the entry is a string and the first three characters are 'np.',
        False otherwise

    """
    if isinstance(val, str):
        if val[0:3] == 'np.':
            return True
        else:
            return False
    else:
        msg = 'entry must be string'
        raise ValueError(msg)