def fields_string(field_type, field_list, sep):
    """Create an error string for <field_type> field(s), <field_list>.
    <sep> is used to separate items in <field_list>"""
    indent = ' '*11
    if field_list:
        if len(field_list) > 1:
            field_str = "{} Fields: ".format(field_type)
        else:
            field_str = "{} Field: ".format(field_type)
        # end if
        fmsg = "\n{}{}{}".format(indent, field_str, sep.join(field_list))
    else:
        fmsg = ""
    # end if
    return fmsg