def Check_Type(poly):
    """Ensures input for polymorphism type is an accepted value

    Parameters
    ----------
    poly : str
        A string representing the type of polymorphism. Either 'SNP' or 'INDEL'
    """
    if poly != 'SNP' and poly != 'INDEL':
        raise ValueError('--type takes only values SNP or INDEL')
    return
