python字典创建

已知路段列表a=['A-B','A-C','A-D','B-C','B-D','C-F'],怎么得出字典b={'A':['B','C','D'],'B':['C','D'],'C':['f']},感谢解答。

代码如下：

a=['A-B','A-C','A-D','B-C','B-D','C-F']

dct = {}
for each in a:
    fisrt,sec = each.split('-')
    if fisrt in dct:
        dct[fisrt].append(sec)
    else:
        dct[fisrt] = [sec]
print(dct)