Simple check if the supplied directory is a SIP directory.

    Parameters
    ----------
    directory: string
        Check if the supplied path is a valid SIP directory


    Returns
    -------
    is_sipdir: bool
        True if the supplied directory is a SIP directory

def is_sipdir(directory):
    """ Simple check if the supplied directory is a SIP directory.

    Parameters
    ----------
    directory: string
        Check if the supplied path is a valid SIP directory


    Returns
    -------
    is_sipdir: bool
        True if the supplied directory is a SIP directory
    """
    is_sipdir = True

    if(not os.path.isfile(directory + os.sep + 'frequencies.dat')):
        is_sipdir = False

    if(not os.path.isdir(directory + os.sep + 'invmod')):
        is_sipdir = False

    return is_sipdir