1def set_doappend(d, var, val, sep=' '):
2    values = (d.getVar(var, True) or '').split(sep)
3    if filter(bool, values):
4        d.appendVar(var, '%s%s' %(sep, val))
5    else:
6        d.setVar(var, val)
7
8
9def listvar_to_list(d, list_var, sep=' '):
10    return list(filter(bool, (d.getVar(list_var, True) or '').split(sep)))
11
12
13def compose_list(d, fmtvar, *listvars, **kw):
14    import itertools
15    fmt = d.getVar(fmtvar, True)
16    lists = [listvar_to_list(d, x) for x in listvars]
17    lst = [fmt.format(*x) for x in itertools.product(*lists)]
18    return (kw.get('sep') or ' ').join(lst)
19
20
21def compose_list_zip(d, fmtvar, *listvars, **kw):
22    fmt = d.getVar(fmtvar, True)
23    lists = [listvar_to_list(d, x) for x in listvars]
24    lst = [fmt.format(*x) for x in zip(*lists)]
25    return (kw.get('sep') or ' ').join(lst)
26